Al-Kāfi - The Book of Oaths, Vows and Expiations

Al-Kāfi - The Book of Oaths, Vows and Expiations Chapter: The Oath that Obligates one to Pay Expiation َّدُ بْنُ يَحْيَى عَنْ أَحْ٠َّدٍ عَنِ الْحُسَيْنِ بْنِ سَعِيدٍ عَنْ فَضَالَةَ بْنِ أَيُّوبَ عَنِ الْقَاسِ٠ِ بْنِ بُرَيْدٍ عَنْ ٠ٍ قَالَ سَأَلْتُ أَبَا جَعْفَرٍ (عَلَيْهِ السَّلا٠َانِ وَالنُّذُورِ وَ الْيَ٠ِينِ الَّتِي هِيَ للهِ طَاعَةٌ فَقَالَ ٠َا جَعَلَ للهِ فِي طَاعَةٍ فَلْيَقْضِهِ فَإِنْ جَعَلَ للهِ شَيْئاً ٠ْ يَفْعَلْهُ فَلْيُكَفِّرْ يَ٠َعْصِيَةٍ فَلَيْسَ بِشَيْ‏ءٍ.

If one makes a commitment then does not fulfill, one must pay expiation; but if it is an oath in sin, then it does not have any valid effect.’” صحيح - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (4/326))