Is expiation obligatory for someone who vowed to fast eight consecutive days, complete a reading of the Quran, donate a sum of money, persevere in prayer, and abandon a sin after succeeding in an exam, then realized that their intention was a bargain with Allah and committed the sin again? And what is the expiation, if obligatory in this case?

According to the majority of scholars, a vow is not binding merely by intention; rather, it is only valid through verbalization, as held by the Shafi'is and Hanbalis. The Malikis have two opinions on the matter. As for the Hanafis, the rules of their madhhab indicate that only a verbally expressed vow is binding. Therefore, internal commitments do not obligate anything, though there is no harm in fulfilling them, or in offering expiation for an oath (kaffarat yameen) in case of inability, in consideration of those who deem the vow binding. It is advisable to avoid such commitments due to the prohibitions mentioned concerning them, and to abstain from sins.