Preliminary topic or field of research: Flour and Oil as Different Categories and Their Ribawī Status.
The First Issue: Flour and Oil as Different Categories
Flour and oil [228] - Like barley flour and wheat flour, and like sesame oil and olive oil. are considered different categories based on their sources. This is agreed upon by the four schools of Islamic jurisprudence: Ḥanafī [229] -"Al-Fatawa Al-Hindiyyah" (3/118), see also: "Bada'i' Al-Sana'i' " by Al-Kasani (5/188). , Mālikī [230] -"Minah Al-Jalil" by 'Ulaysh (5/10), see also: "Sharh Mukhtasar Khalil" by Al-Kharashi (5/60), and "Tahdhib Al-Furuq" by Ali ibn Hussain Al-Maliki (3/269). , Shāfiʿī [231] -"Minhaj Al-Talibin" by Al-Nawawi (p. 96), " Mughni Al-Muhtaj" by Al-Shirbini (2/23), and "Nihayat Al-Muhtaj" by Al-Ramli (3/431) , and Ḥanbalī [232] - "Kashshaf Al-Qina'" by Al-Buhuti (3/255), and " Matalib Uli Al-Nuha" by Al-Ruhaybani (3/161). . This is because the derivative follows its origin, so since the sources of these are different categories, the derivatives must also be different categories, following the principle of attaching derivatives to their sources [233] -"Kashshaf Al-Qina'" by Al-Buhuti (3/255). .
The Second Issue: Flour and Oil as Ribawī (Usurious) Commodities
Flour and oil are considered among the commodities subject to ribā (usury) because they are both consumable and measured by volume. The rulings on selling flour and oil will be discussed in the following sections.
The First Topic: Selling Flour and Oil of the Same Category
It is not permissible to sell flour and oil from the same source for one another with disparity in quantity, such as selling barley flour for barley flour or olive oil for olive oil with unequal quantities. It is permissible, however, to sell them equally in quantity and hand to hand. This is the view of the majority of scholars [234] - The Shafi'i scholars ruled the prohibition of selling flour for the same kind in equal measure,  while they permitted the sale of oil for the same kind in equal measure. "Minhaj Al-Talibin" by    Al-Nawawi (p. 96), and " Mughni Al-Muhtaj" by Al-Shirbini (2/26). : Ḥanafī [235] -" Al-Fatawa Al-Hindiyya" (3/118), see also: " Bada'i' Al-Sana'i' " by Al-Kasani (5/188). , Mālikī [236] - "Minah Al-Jalil" by 'Ulaysh (5/10), see also: " Tahdhib Al-Furuq"by Ali ibn Hussain Al-Maliki  (3/269). , and Ḥanbalī [237] - " Kashshaf Al-Qina' " by Al-Buhuti (3/255), and " Matalib Uli Al-Nuha" by Al-Ruhaybani (3/161). . This is because the derivative follows its origin, and since their sources are considered different categories, these derivatives must also be treated as such. Therefore, selling the same category for the same category with disparity is not allowed [238] - " Kashshaf Al-Qina' " by Al-Buhuti (3/255) .
The Second Issue: Selling Flour and Oil from Different Categories
It is permissible to sell flour and oil from different sources for one another with disparity, as long as the exchange is done hand to hand, such as barley flour for wheat flour or olive oil for sesame oil with disparity in quantity, provided the transaction is immediate, means hand to hand . The four schools of Islamic jurisprudence agree upon this: Ḥanafī [239] -" Al-Fatawa Al-Hindiyya" (3/118), see also: " Bada'i' Al-Sana'i' " by Al-Kasani (5/188). , Mālikī [240] -((Minhaj Al-Jalil)) by 'Ulaysh (5/10), see also: " Tahdhib Al-Furuq"by Ali ibn Hussain Al-Maliki (3/269). , Shāfiʿī [241] -"Minhaj Al-Talibin "by Al-Nawawi (p. 96), " Mughni Al-Muhtaj" by Al-Shirbini (2/23), and " Nihayat Al-Muhtaj " by Al-Ramli (3/431) , and Ḥanbalī [242] - " Kashshaf Al-Qina' " by Al-Buhuti (3/255), and " Matalib Uli Al-Nuha" by Al-Ruhaybani (3/161). .
Reasoning:
Firstly, the derivative follows its source, so since their sources are different categories, these derivatives are also different categories, following the principle of attaching derivatives to their sources [243] - See: "Tahthib Al-Furuq"by Ali ibn Hussain Al-Maliki (3/269) .
Secondly, they differ in their essence, and sharing the same general name—such as "flour" or "oil"—does not necessitate their unity in category, just as wheat and barley both share the name "grain," yet they are not unified in category [244] - See: ” Al-Majmu' '"by Al-Subki (10/181). .
Thirdly, the Arabs did not assign a specific name to each type of flour; instead, it sufficed with the general name, which was distinguished by the addition of its source. This does not necessitate unity in the category, and the difference in their realities stems from different sources, necessitating that they be treated as distinct, as their origins differ [245] - see: the previous reference. .
The Third Topic: Selling Wheat for Flour or Sawiq of the Same Category
Note: Sawiq is kind of food made of fine flour.
Discussion on Selling Wheat for Flour or Sawiq of the Same Category:
Scholars have differed regarding the ruling on selling wheat for flour or Sawiq of the same category, with two opinions:
The First Opinion: It is not permissible to sell wheat for flour or Sawiq of the same category [246] -Al-Suwaq: It is wheat (or barley) that is roasted, then ground, and then mixed with dates or something similar. See: "Fath Al-Bari " by Ibn Hajar (1/135), and " Majmu' Fatawa wa Rasail Ibn Uthaymeen " (9/423) , even if they are equal in weight. This is the view of the majority, including the Ḥanafī [247] - "Al-Bahr Al-Ra'iq" by Ibn Nujaym (6/14), and " Al-Fatawa Al-Hindiyya" (3/118) , Shāfiʿī [248] - " Fath Al-Aziz "by Al-Rafi'i (8/180), and " Rawdat Al-Talibin " by Al-Nawawi (3/387). , and Ḥanbalī schools [249] - " Al-Furu' " by Ibn Muflih (6/303), and " Kashshaf Al-Qina' " by Al-Buhuti (3/255). , and it is also an opinion of some Mālikīs [250] -"Minhaj Al-Jalil" by 'Ulaysh (5/23), see also:"Tahdhib Al-Furuq"by Ali ibn Hussain Al-Maliki (3/270). .
The reasoning
Firstly: Selling wheat for flour sawiq is considered selling wheat for its own kind with disparity in quantity, which is prohibited. This is because milling has separated its parts, leading to differences in measurement between the flour and the wheat. Even if disparity does not occur, the equality cannot be confirmed; ignorance of equality is akin to knowledge of disparity in matters where equality is required [251] - see: the previous reference. .
Secondly: Selling wheat for "Sawiq" is also seen as selling wheat for its own kind with disparity, thus it is prohibited. This is because the fire has affected one of them differently than the other, preventing the confirmation of equality.
The Second Opinion: It is permissible to sell wheat for flour and sūwīq of the same category as long as they are equal in weight. This is the view of the Mālikī school [252] -"Minhaj Al-Jalil" by 'Ulaysh (5/23); See: " Tahdhib Al-Furuq"by Ali ibn Hussain Al-Maliki (3/270). and a narration from Aḥmad [253] - "Al-Insaf" by Al-Mardawi (5/23), see:"Al-Mughni" by Ibn Qudamah (4/21). , as well as the opinion of some of the Salaf [254] - See: ((Al-Mughni)) by Ibn Qudamah (4/21). , which Ibn ʿUthaymīn [255] - Ibn 'Uthaymin said: “His statement: ‘It is not permissible to sell grain for its flour,’ even if they are equal in weight... Some scholars have said that if they are equal in weight, there is no harm; because their equality in weight indicates their equality in measurement as grain... This opinion is correct, because the similarity is present, and necessity calls for exchanging this for that, or the flour can be converted back to grain, using a scale.” ((Al-Sharh Al-Mumti')) (8/414). also chose. This is because flour is essentially the same as wheat; it has merely been broken into parts, allowing for the sale of some for others, similar to broken wheat being sold with whole wheat.
The Fourth Topic: Selling Wheat Bread for Wheat, and Barley Bread for Barley
Scholars have differed regarding the ruling on selling bread made from wheat for wheat and bread made from barley for barley, with two opinions:
The First Opinion: It is permissible to sell bread made from wheat for wheat and bread made from barley for barley, whether with disparity or equality. This is the view of the Ḥanafīs [256] -"Tabyeen Al-Haqa'iq" by  Al-Zaylai (4/95); " Al-Bahr Al-Ra'iq " by Ibn Nujaym (6/146); "Hashiyat Ibn Abidin"  (5/182); " Al-Fatawa Al-Hindiyyah " (3/118). and Mālikīs [257] - " Al-Kafi" by Ibn Abd al-Bar (2/651); "Al-Taj wa al-Ikleel " by Al-Mawaaq (4/355); " Sharh al-Zurqani 'ala Mukhtasar Khalil " (5/124). , and it was chosen by Ibn Taymiyyah [258] -Ibn Taymiyyah said: "It is permissible to sell items made of gold and silver for their own kind without requiring them to be equal in weight. The excess can be taken in exchange for the item itself, which is not considered riba (usury) nor of the same kind in itself. For example, bread can be exchanged for harisa, and oil for olives, and sesame for small seeds. As for items made of brass and iron—if we say that riba applies to them—it will also apply to the finished product if it is intended to be weighed after fabrication, such as silk garments and similar items; otherwise, it does not." "Al-Fatawa al-Kubra" (5/391- 392). and Ibn al-Qayyim [259] - Ibn al-Qayyim said: "If it is said: You are therefore required to permit the sale of the branches of the species for their roots with a difference in measure, such as permitting the sale of wheat for bread with a difference in measure, oil for olives, and sesame for shirjeh. It is said: This is indeed a valid question, and the answer is that the prohibition is only established by a text, consensus, or = = the prohibited form being equivalent in every way to what is specified as prohibited. The three conditions are absent in the branches of the species in comparison to their roots... It is not prohibited to sell them for another kind even if they belong to the same species; thus, the sale of sesame for shirjeh is not prohibited, nor the sale of harisa for bread; for this trade has value and is not wasted on its owner. There is no prohibition against selling it for its roots in any book, sunnah, =consensus, or analogy, and nothing is prohibited except what Allah has made unlawful." (( I'lam al-Muwaqqi'in" by Ibn al-Qayyim (2/111)) .
Reasoning:
Firstly: Bread has become a different category due to the process of production, thus it is no longer measured by volume. Wheat and flour are measured by volume, and since the measure and the category do not unify them, it is permissible to sell one for the other on credit, provided the wheat is the delayed item, as it can be controlled [260] -"Taj wa al-Iklil" by al-Muwaq (4/355); "Tabyin al-Haqaiq" by al-Zaylai (4/95) .
Secondly: Wheat is a measured commodity, while flour and bread are measured by weight. Thus, it is permissible to sell one for the other with disparity or equality if they are treated as currencies, even if one is a credit transaction; if the bread is a currency, it is also permissible [261] -"Fatāwā al-Hindiyyah" by al-Marghīnānī (3/118). .
The Second Opinion: It is not permissible to sell bread made from wheat for wheat and bread made from barley for barley, whether with disparity or equality. This is the view of the Shāfiʿī [262] -"Tuhfat al-Muhtāj" by Ibn Ḥajar al-Haythamī (4/281), and see: "Al-Ghurar al-Bahiyyah "by Zakariyā al-Anṣārī (5/130), al-Majmūʿ by al-Subkī (11/122). and Ḥanbalī schools [263] -See: "Kashaf al-Qinaʿ " by al-Buhūtī (3/256). , as well as a narration from Abū Ḥanīfah [264] -"Tabyin al-Haqaiq" by al-Zaylai (4/95). , and it was chosen by Ibn ʿUthaymīn as a precaution [265] - Ibn Uthaymin said: "Flour is a type in terms of its original substance, as are loaves of bread. If you wish to sell bread made from wheat for barley grits — and barley grits are grains that have been ground but not finely milled — this is not permissible due to the impossibility of equal exchange. And Shaykh al-Islam may Allah have mercy on him said: What is made from these types; if it is no longer a staple food due to this processing, it is no longer considered to be subject to usury, based on the fact that the reason for usury is the nature of it being a staple food. If it does not change, then it remains an independent type that is not dependent on its original substance. Accordingly, it is permissible for me to sell bread made from wheat for barley grits made from wheat, as each one has clearly different characteristics, both in terms of consumption and intent. Thus, it becomes an independent type. However, caution is what the author, may Allah have mercy on him,=  =recommended due to the generality of his saying, peace and blessings be upon him: ‘Wheat for wheat, equal for equal,’ which includes wheat in any condition. And ‘barley for barley’ also includes barley in any condition. "  "Sharh al-Mumt'I" by Ibn Uthaymin (8/408). .
The reasoning is as follows:
Firstly: Due to the differences and varying effects of fire on the bread [266] -"Mughni al-Muhtaj "by al-Shirbini (2/26). .
Secondly: Because it is impossible to ascertain equality, and ignorance of equality is akin to knowledge of disparity [267] -"Iqna'" by al-Shirbini (2/282), "Kashaf al-Qina' "by al-Buhuti (3/256). .
The Fifth Topic: Selling Bread for Bread
It is permissible to sell bread for bread [268] - It is permissible to sell bread for bread of the same kind, such as barley bread for barley bread, or wheat bread for wheat bread, or from different kinds, such as selling wheat bread for barley bread. of the same kind, equal in measure, whether dry or moist. If they are of different kinds, disparity is allowed, but selling them on credit [269] -That is: the deferred sale. is prohibited . This is the view of the Ḥanbalīs [270] -"Al-Insaf "by Al-Mardawi (5/25), Sharh Muntaha Al-Iradat by Al-Buhuti (2/67). .
Reasoning:
Firstly: If one of them is moister than the other, equality, which is a condition, cannot be achieved. The comparison in dryness refers to the baked product, and equivalence should be by weight, as measuring by volume is impractical [271] - "Al-Mubdi'" by Burhan Al-Din Ibn Muflih (4/135) .
Secondly: It is prohibited to separate and leave the place of transaction before taking possession, as they are from different kinds while sharing the same reason for prohibition [272] - "Al-Mughni "by Ibn Qudamah (4/10). .