What is the ruling regarding someone who vowed to slaughter two sheep on a specific date, but was unable to fulfill it on that date due to unforeseen circumstances? Should the vow be postponed to the wedding anniversary in the following year, or should he slaughter them when he is able to do so? Is there an expiation for delaying it?

If the vow to slaughter is for drawing closer to Allah, then it is an act of worship that must be fulfilled. If its specified time has passed, it does not lapse, and the slaughter must still be performed along with an expiation for an oath (kaffarat yameen) for the delay. However, if the vow was for eating or for something permissible (mubah), then it is not considered binding according to the Hanafis and some Malikis and Shafi'is, and this is the relied-upon opinion (al-mufta bihi). The Hanbalis and some Malikis hold that it is binding, but one has the choice between performing it or not, and if one does not fulfill it, an expiation for an oath is due. The expiation for an oath is feeding ten poor persons, or clothing them, or freeing a slave. If one cannot find any of these, then fasting for three days.