What is the ruling on vowing to perform a permissible act (Mubah)?
General Chapter
Al-Mughni
Book of Vows
Primary text
For a vow concerning a permissible act, such as riding one's beast, residing in one's house, or divorcing one's wife permissibly, the vow-maker has the choice: either to perform the act and thereby fulfill the vow, or to refrain from it and offer the expiation of an oath. Fulfillment is supported by the case where a woman vowed to beat a drum on the Prophet's head, and he commanded her to fulfill it, likening the vow to an oath that is fulfilled by performance.
Supporting text
Some scholars argue that no expiation is due if the permissible act is omitted, pointing to cases where fulfilling a vow concerning a specific mosque or giving all one's wealth allowed for alternatives or omission without expiation. Others, like Malik and Shafi'i, hold that such a vow is invalid because it does not seek the Face of Allah.