What is Kaffarah Nazar كفارة النذر ?
A person vows to perform a deed if a desired outcome is attained (e.g., pass an exam). In a situation where the person is unable to fulfill his vow, he has to offer Kafarah Nazar (i.e., feed or clothe 10 poor persons). If he is unable to do this, he has to fast for 3 days for Allah.
Example: Ahmad vowed that if he passed his exam, he will perform Umrah in Ramadhan this year. However, although his exam results were positive, he was unable to perform Umrah in Ramadhan this year. Therefore, he has to offer Kafarah Nazar.
Evidence for Kaffarah Nazar كفارة النذر
يُوفُونَ بِالنَّذْرِ وَيَخَافُونَ يَوْمًا كَانَ شَرُّهُ مُسْتَطِيرًا
They (are those who) fulfill (their) vows, and they fear a Day whose evil will be wide-spreading. (Surah Al-Insan, verse 7)
Ibn ‘Abbaas (may Allaah be pleased with them both) said, “Whoever makes a vow and is then unable to fulfil it, his expiation is kafaarat yameen. (Feed or Cloth 10 poor persons)” (Reported by Abu Dawood)