Is it permissible to make a vow to fast days as expiation for a repeated sin in order to deter oneself from it?
Undertaking a vow is dislikable (makruh). This type of vow is called a "vow of obstinacy" (nadhr al-lajaj). A Muslim must fear Allah and keep away from disobeying Him. If a Muslim breaks this vow, he must offer an expiation for an oath (kaffarat yamin) instead of fasting, according to the more preponderant opinion. Alternatively, he has the choice between expiation and fulfilling the vow, according to some scholars. Fulfilling the vow does not expiate the sin; rather, repentance from the sin is required by abandoning it, regretting it, and resolving not to return to it.
Summarized from the full answer at Ftawy · reviewed Sep 2, 2026
Read the full answer on Ftawyhttps://ftawy.com/en/questions/78099