Furthermore, the basis of contracts is the consent of the contracting parties, and their binding effect consists in what the parties have bound themselves to through their agreement. For Allah says in His Mighty Book:
“Except through trade by mutual consent among you.”
And He says:
“But if they willingly give up to you any part of it, then enjoy it with pleasure and satisfaction.”
He thus made permission to consume it dependent upon willing consent, as a consequence depends upon its condition. This indicates that willing consent is a cause of that permission. Here, a ruling is made contingent upon a relevant attribute expressed in a derivative form, indicating that this attribute is the cause of the ruling.
If willing consent permits the consumption of the bridal gift, the same applies to all other gratuitous transfers, by analogy with it on the basis of the effective cause explicitly indicated by the Quran.
Likewise, in His words:
“Except through trade by mutual consent among you,”
no condition is stipulated for trade other than mutual consent. This entails that mutual consent is what makes trade permissible. Accordingly, when the contracting parties mutually consent to a commercial transaction, or a donor willingly makes a gift, its permissibility is established by the Quran—unless it involves something Allah and His Messenger have forbidden, such as trading in wine and the like.
Furthermore, a contract may be either unqualified or qualified by stipulations. There is a distinction between an unqualified contract and the concept of a contract as such. Thus, if someone says, “This condition conflicts with what the contract entails,” and means that it conflicts with an unqualified contract, then the same is true of every additional condition, and this does not impair the contract. But if he means that it conflicts with what the contract entails whether unqualified or qualified, evidence is required to establish that claim. Such a claim is valid only when the condition conflicts with the purpose of the contract.