What is Kaffarah Yameen كفارة اليمين ?
A Muslim made an oath by the name of Allah (Wallahi) to perform an act, but he did not fulfil his oath. To repent for his mistake, he has to offer a Kafarah Yameen, by feeding or clothing 10 poor persons. If he is unable to do this, he has to fast for 3 days for Allah.
Example: Ahmad said: “Wallahi (By Allah) I will perform Solat Al-Isha in Masjid Al-Haram today.” But Ahmad was unable to perform Solat Al-Isha in Masjid Al-Haram today. Therefore, he has to offer Kaffarah Yameen.
Evidence for Kaffarah Yameen كفارة اليمين
لَا يُؤَاخِذُكُمُ اللَّهُ بِاللَّغْوِ فِي أَيْمَانِكُمْ وَلَٰكِن يُؤَاخِذُكُم بِمَا عَقَّدتُّمُ الْأَيْمَانَ ۖ فَكَفَّارَتُهُ إِطْعَامُ عَشَرَةِ مَسَاكِينَ مِنْ أَوْسَطِ مَا تُطْعِمُونَ أَهْلِيكُمْ أَوْ كِسْوَتُهُمْ أَوْ تَحْرِيرُ رَقَبَةٍ ۖ فَمَن لَّمْ يَجِدْ فَصِيَامُ ثَلَاثَةِ أَيَّامٍ ۚ ذَٰلِكَ كَفَّارَةُ أَيْمَانِكُمْ إِذَا حَلَفْتُمْ ۚ وَاحْفَظُوا أَيْمَانَكُمْ ۚ كَذَٰلِكَ يُبَيِّنُ اللَّهُ لَكُمْ آيَاتِهِ لَعَلَّكُمْ تَشْكُرُونَ
Allah will not impose blame upon you for what is meaningless in your oaths, but He will impose blame upon you for [breaking] what you intended of oaths. So its expiation is the feeding of ten needy people from the average of that which you feed your [own] families or clothing them or the freeing of a slave. But whoever cannot find [or afford it] – then a fast of three days [is required]. That is the expiation for oaths when you have sworn. But guard your oaths. Thus does Allah make clear to you His verses that you may be grateful.
(Surah Al-Maidah, Verse 89)