Al-Kāfi

Hadith 571
fastingexpiation
4ـ أَبُو عَلِيٍّ الأَشْعَرِيُّ عَنْ مُحَمَّدِ بْنِ عَبْدِ الْجَبَّارِ عَنْ صَفْوَانَ بْنِ يَحْيَى عَنْ عِيصِ بْنِ الْقَاسِمِ قَالَ سَأَلْتُهُ عَمَّنْ لَمْ يَصُمِ الثَّلاثَةَ الأَيَّامِ مِنْ كُلِّ شَهْرٍ وَهُوَ يَشُدُّ عَلَيْهِ الصِّيَامُ هَلْ فِيهِ فِدَاءٌ قَالَ مُدٌّ مِنْ طَعَامٍ فِي كُلِّ يَوْمٍ.
4. Abu Ali al-Ash’ariy has narrated from Muhammad ibn ‘Abd al-Jabbar from Safwan ibn Yahya from ‘Is ibn al-Qasim who has said the following: “I once asked him (the Imam) (a.s.), about a man who does not fast three days every month because fasting is difficult for him: if there is a ransom for it. He (the Imam) said, ‘It is one mud (a certain measurement) of food for everyday.’”
Source: Shaykh Muḥammad b. Yaʿqūb al-Kulaynī