Section 1: Valid stipulations:

Firstly: Stipulating things that are intrinsic to the contract
Stipulating things that are intrinsic to the contract is permissible

Evidence:
(1) Scholarly Consensus
A consensus on this issue was related from al-Maziri, Ibn al-Qayyim, Ibn Qudamah, who said that it does not affect the contract, and Nawawi.
(2) Because it emphasises and clarifies what the contract entails.
(3) Because the default position regarding contracts and conditions is permissibility and validity. Prohibition and invalidation only occur when indicated by an explicit text or through analogical reasoning for those who accept that method.

Secondly: Stipulating a characteristic of the commodity
Stipulating a characteristic of the commodity is valid.
Evidence:
(1) Scholarly Consensus
A consensus on this issue was related from Ibn Qudamah, Ibn Taymiyyah, and Mardawi.
(2) Because this stipulation is merely an obligation related to an existing matter at the time of the contract and is not contingent on the establishment of a future event, so it is valid.
(3) Because the default position regarding contracts and conditions is permissibility and validity. Prohibition and invalidation only occur when indicated by an explicit text or through analogical reasoning for those who accept that method.

Thirdly: Stipulating things related to the benefit of the two parties to the contract
Stipulating things related to the benefit of the two parties to the contract, such as the term of the agreement, option to annul the agreement, collateral security, and guarantee of the commodity is permissible.
Evidence:
(1) Scholarly Consensus
A consensus on this issue was related from Ibn Qudamah, Ibn al-Qayyim, Nawawi, and al-Kamal ibn al-Humam.
(2) Because the default position regarding contracts and conditions is permissibility and validity. Prohibition and invalidation only occur when indicated by an explicit text or through analogical reasoning for those who accept that method.

Fourthly: Stipulating a benefit for one of the parties in a trade 
Stipulating a benefit for one of the parties in a trade is valid, and this was the position of the Malikis and Hanbalis , a view of the Shafi`is, the view of a group of the predecessors, and the preferred opinion of Bukhari, Ibn al-Mundhir, Ibn Taymiyyah, Ibn al-Qayyim, San`ani, and Ibn `Uthaymin.
Evidence:
(1)
From the Sunnah
Jabir narrated that he was riding a camel that had become exhausted. The Prophet passed by, struck it, and supplicated for him. The camel then started walking with a pace like no other. Jabir narrated, “The Prophet then said, ‘Sell it to me for one uqiyyah.’ ‘No’, I replied. ‘Sell it to me for one uqiyyah,’ he repeated. So, I sold it, but I excluded riding it back to my family. When we arrived, I brought the camel to him, and he gave me its price. I then left, but he sent someone after me, and when I got back to him he said, ‘I would not have taken your camel. Take that camel of yours, for it is your property.’” Shu`bah narrated from Mughirah, from `Amir, from Jabir, “The Messenger of Allah lent me the camel’s back until Medina.” Jabir excluded the riding of the camel back to his family for himself, which was a benefit of the commodity. The Prophet did not object to this; rather, he allowed it and did not invalidate the trade.
(2) Because most of what is delayed in its delivery has a known duration, so it is valid, as would be the case with selling a rented house.
(3) As would be the case with someone selling a date palm tree with unripe fruits and excluding the fruits for himself, the trade is valid, and the fruits remain on the palm tree until they ripen, and this is an exclusion for the benefit of the seller.
(4) Because the default position regarding contracts and conditions is permissibility and validity. Prohibition and invalidation only occur when indicated by an explicit text or through analogical reasoning for those who accept that method.

Fifthly: Stipulating a contract other than a loan in a sales agreement 
Stipulating a contract other than a loan in a sales agreement is permissible, and this was the view of Ashhab from the Malikis and the preferred opinion of Ibn Taymiyyah, Ibn al-Qayyim, and Ibn `Uthaymin.
Evidence:
(1)
From the Book:
The Statement of Allah Exalted, “O believers! Honour your obligations.”
Allah Exalted commanded the honouring of obligations, and this is a general command with no exclusions, unless there is a specific proof indicating an exception.
(2) Because when honouring and upholding covenants is commanded, it is known that the default position regarding contracts and stipulations is validity. There is no meaning in validation unless it leads to the intended result and accomplishes its purpose, and the purpose of a contract is its fulfilment.
(3) Because contracts and conditions fall under the category of ordinary actions, and the default status for them is non-prohibition. The absence of prohibition is presumed until there is evidence indicating prohibition. Prohibition and invalidation only occur when the Shariah indicates this through an explicit text or through analogical reasoning for those who accept that method.
(4) Because when a permissible contract includes two separate matters (i.e., two separate contracts), each of them is also individually permissible.

Sixthly: Multiple valid stipulations in a trade
It is valid to have multiple stipulations in a trade, even if they are connected to the benefit of one of the parties, and this was a statement related from Ahmad and the preferred opinion of Ibn Taymiyyah, Ibn al-Qayyim, and Ibn `Uthaymin.
This is for the following reasons: 
(1) Because the default position regarding contracts and conditions is permissibility and validity. Prohibition and invalidation only occur when this is indicated through an explicit text or analogy.
(2) Because valid conditions do not affect the sale even if they are numerous, whilst an invalid one does even if it is singular.

Seventhly: Stipulating the option to annul a trade for a known duration, even if it is lengthy
Stipulating the option to annul a trade for a known duration, even if it is lengthy, is permissible.

Eighthly: Penalty clauses in contracts
(1) Defining a “penalty clause”
The penalty clause is an agreement between the contracting parties to determine the compensation that one is entitled to if the other party causes harm by failing to fulfil or delaying in fulfilling their commitment.
(2) Ruling on penalty clauses in exchange for delaying work
It is permissible to stipulate a penalty clause in exchange for delaying work, and this was the view of some of the predecessors, the preferred opinion of Bukhari and Abu al-Layth al-Samarqandi from the Hanafis, and the decision of the Islamic Fiqh Academy, the Council of Senior Scholars, and the Al-Azhar Islamic Research Academy.
Evidence:
(A) From the Quran:
The Statement of Allah Exalted, “O believers! Honour your obligations.”
(B) From the Sunnah:
The generality of the statement of the Prophet, “Muslims are bound by their stipulations.”
(C) From narrations:
`Umar ibn al-Khattab said, “Indeed, rights are subject to stipulations, and you are entitled to that which you stipulate.”
(D) Because violating contracts causes harm and loss of benefits, so it is appropriate for that to be countered by a penalty clause.
(E) Because the default position regarding stipulations is that they are valid.
(F) The penalty clause closes the doors to chaos and violation of the rights of the servants of Allah.
(G) The penalty clause acts as an incentive to complete contracts within their specified time and honour agreements.
(3) Ruling on penalty clauses in exchange for delaying the repayment of a debt
A penalty clause is not permissible in contracts in which the original obligation was a debt, and this was stated by the Islamic Fiqh Academy and the Al-Azhar Islamic Research Academy This is because it is considered an additional debt, and stipulating an increase in a debt due to a delay in repayment is outright usury.