What should I do regarding the vow I made to slaughter animals and feed the battalion, which I vowed for my cousin's release from prison, knowing that I have not fulfilled it and the battalion has moved to another location? Should I offer expiation for that?

Scholars have differed regarding the validity of a vow concerning a permissible act. Ahmad held that the vower has the choice between performing the act or offering an expiation for a broken oath (kaffarat yamin). However, the Malikis held that such a vow is not binding and nothing is required for it, and this is the more correct opinion. Feeding colleagues and friends falls under this category, so no expiation or fulfillment is necessary. Nevertheless, offering an expiation for a broken oath is more cautious, as it avoids the disagreement.