Engaging in two sales in one transaction is not permissible, nor valid [335] - In its interpretation, it is mentioned that there are various opinions; it is said that it refers to selling at a deferred price on the condition that it is bought back at a lower immediate price, which is the issue of the sale of ʿInah.       It is also said that it refers to a man selling a commodity for ten in cash or for twenty on credit, and the two parties part without specifying which of the two prices is applicable. See: "Al-Majmūʿ " by al-Nawawī (9/338); "Al-Infāf " by al-Mardāwī (4/225); "Majmūʿ al-Fatāwā" by Ibn Taymiyyah (29/447); "Sharḥ al-Mumtiʿ" by Ibn ʿUthaymīn (8/238). .
The Evidences:
Firstly: From the Sunnah:
On the authority of Abu Hurayrah رضي الله عنه he said: “The Messenger of Almighty Allah صلى الله عليه وسلم forbade two sales in one transaction. [336] - It was narrated by al-Tirmidhī (1231); al-Nasā'ī (4632), and Aḥmad (9584).       Al-Tirmidhī said: “Hasan ṣaḥīḥ” (good and authentic), and Ibn ʿAbd al-Barr stated in "Al-Istithkār" (5/458).      “A connected and authentic chain transmitted by reliable narrators.” Ibn al-ʿArabī authenticated it in ((Al-Qabas)) (2/842); al-Nawawī in "Al-Majmūʿ " (9/338); and Ibn al-Mulaqqin in "Al-Badr al-Munīr" (6/496). Al-Albānī stated in "Ṣaḥīḥ Sunan al-Nasā'ī" (4632): "Hasan ṣaḥīḥ" (good and authentic); and "al-Wādiʿī " considered it Hasan in "Al-Ṣaḥīḥ al-Musnad" (1383). ”
Reasoning:
The ambiguity in the price is included in the meaning of two sales in one, and thus it falls under the prohibition mentioned in the hadith [337] - See: "al-Mubdiʿ " by Burhān al-Dīn Ibn Mufliḥ (3/373). .
Secondly : From Ijma' (Consensus):
Ibn Rushd al-Hafid [338] - Ibn Rushd al-Ḥafīd said: “As for what is explicitly stated in the sharʿ, among it is: ‘His prohibition, may Allah’s peace and blessings be upon him, of selling the fetus of a pregnant animal,’ and among it is: ‘His prohibition of selling what has not been created,’ and ‘of two sales in one sale’... All of these are pre-Islamic sales unanimously agreed upon to be prohibited.” " Bidayat al-Mujtahid" (3/167) and Imam al-Nawawi [339] - Al-Nawawī said: “Al-Shāfiʿī and other scholars explained the two sales in one sale in two ways; one of them is that he says: ‘I sold you this for ten in cash, or for twenty on credit,’ and the second is that he says: ‘I sold it to you for a hundred— for example— on the condition that you sell me your house for so much.’ The author mentioned both interpretations in the following chapter, and they are also mentioned in ‘Al-Tanbīh,’ and by the companions and others. The first interpretation is more well-known, and in either case, the sale is invalid by consensus.” "Al-Majmūʿ " (9/338). reported this consensus.
Thirdly: Because the contract was not made on a specific price, it is like saying: “I sell you either of these two items. [340] - See: "Al-Muhathab"  by al-Shīrāzī (2/19) ”