Chapter on the Recommended Fasts of the Year
Man Lā Yaḥḍuruh al-Faqīh|Volume 2|Book 2|Chapter 4
وَ رَوَى اِبْنُ مُسْكَانَ عَنْ إِبْرَاهِيمَ بْنِ اَلْمُثَنَّى قَالَ: قُلْتُ لِأَبِي عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ إِنِّي قَدِ اِشْتَدَّ عَلَيَّ صَوْمُ ثَلاَثَةِ أَيَّامٍ فِي كُلِّ شَهْرٍ فَمَا يُجْزِي عَنِّي أَنْ أَتَصَدَّقَ مَكَانَ كُلِّ يَوْمٍ بِدِرْهَمٍ فَقَالَ «صَدَقَةُ دِرْهَمٍ أَفْضَلُ مِنْ صِيَامِ يَوْمٍ ».
It is narrated by Ibn Muskan from Ibrahim ibn al-Muthanna, who said: "I said to Abu Abdullah (Imam Jafar ibn Muhammad Al-Sadiq عليه السلام): 'Fasting three days every month has become difficult for me. What would suffice for me? Can I give charity in place of each day, a dirham?' Imam عليه السلام said: 'Giving charity of a dirham is better than fasting a day.'"
- Ṣaḥīḥ al-Faqīh