Chapter on Vows
There is no expiation for a specified vow other than fulfilling it.
Vows are of two kinds: a vow made in obedience to Allah, which must be carried out, and a vow made in disobedience to Allah, which requires neither fulfillment nor expiation.
A vow of obedience may be unconditional, or it may be linked to a particular condition or circumstance.
The unconditional vow is like one’s saying, “It is incumbent upon me, for Allah’s sake, to perform Hajj, to pray, to fast, to free a slave, or to give charity,” and similar acts of righteousness; such a vow must be fulfilled.
The conditional vow becomes binding once the stipulated condition or circumstance actually occurs.