What is the method for fulfilling a vow to study the exegesis (Tafsir) of the Holy Quran after graduating from university, given the uncertainty as to whether the vow was for the supplementary course or the initial one, and is it permissible to offer expiation (kaffarah) instead of fulfilling the vow?

One must fulfill a vow exactly as it was vowed, based on the Almighty's saying: {and let them fulfill their vows}. Studying the interpretation of the Qur'an is among the greatest acts of devotion. If the specific type of study is forgotten, the one who made the vow must strive to remember it. If it cannot be ascertained, then the more cautious approach should be taken. If the first course was broader or more comprehensive, it should be taken as a precaution and to clear one's conscience. It is not permissible to change the vow to an expiation as long as the person is able to fulfill it. However, if one becomes permanently unable to fulfill it, then he must offer an expiation for an oath, as the Prophet (peace be upon him) said: "The expiation for a vow is the expiation for an oath." The expiation for an oath is feeding ten poor people, or clothing them, or freeing a believing slave. If one cannot find any of these, then fasting three days.