Ahmad’s explicit statements and principles, and that held by his early followers—as is also the position of the scholars of Medina—is that a stipulation made before a contract is equivalent to one made contemporaneously with it. Thus, if the parties agree on something and subsequently conclude the contract, it is construed in light of what is known between them—namely, what they had agreed upon. Similarly, references to dirhams and dinars in contracts are construed according to what is customarily understood between them, just as all contracts are construed according to the mutual understanding of the contracting parties.

[Chapter: The Fifth Principle Concerning Oaths and Vows]
[Preliminaries of Great Benefit in This Chapter]
[The First Preliminary: Questions Concerning Oaths Relate Either to the Ruling on What Is Invoked in the Oath or to the Ruling on the Matter Sworn To]

Chapter

The Fifth Principle Concerning Oaths and Vows

Allah Most High says:

“O Prophet! Why do you forbid what Allah has made lawful for you, seeking to please your wives? Allah is All-Forgiving, Most Merciful. Allah has already prescribed for you the means of release from your oaths. Allah is your Protector, and He is the All-Knowing, the All-Wise.” [al-Tahrīm: 1–2] [al-Tahrīm]

And He, Most High, says:

“Do not make Allah, through your oaths, an obstacle to doing good, being mindful of Him, and making peace among people. Allah is All-Hearing, All-Knowing.” [al-Baqarah: 224] [al-Baqarah: 224]

And He, Most High, says:

“Allah will not hold you accountable for thoughtless oaths, but He will hold you accountable for what your hearts have earned. Allah is All-Forgiving, Most Forbearing. Those who swear to abstain from their wives must wait four months. If they resume marital relations, then Allah is All-Forgiving, Most Merciful. But if they resolve upon divorce, then Allah is All-Hearing, All-Knowing.” [al-Baqarah: 225–227] [al-Baqarah]

And He, Most High, says:

“O you who believe! Do not forbid the wholesome things Allah has made lawful for you, and do not transgress. Indeed, Allah does not love transgressors. Eat of the lawful and wholesome things Allah has provided for you, and fear Allah, in whom you believe. Allah will not hold you accountable for thoughtless oaths, but He will hold you accountable for the oaths by which you deliberately bind yourselves. Their expiation is to feed ten needy people with food of the average kind you provide for your families, or to clothe them, or to free a slave. Whoever cannot afford this must fast for three days. That is the expiation for your oaths when you swear. Guard your oaths. Thus does Allah make His signs clear to you, so that you may give thanks.” [al-Mā’idah: 87–89] [al-Mā’idah].