Chapter on the Recommended Fasts of the Year
Man Lā Yaḥḍuruh al-Faqīh|Volume 2|Book 2|Chapter 4
وَ قَالَ أَمِيرُ اَلْمُؤْمِنِينَ عَلَيْهِ اَلسَّلاَمُ: «صِيَامُ شَهْرِ اَلصَّبْرِ وَ ثَلاَثَةِ أَيَّامٍ مِنْ كُلِّ شَهْرٍ يَذْهَبْنَ بِبَلاَبِلِ اَلصَّدْرِ وَ صِيَامُ ثَلاَثَةِ أَيَّامٍ فِي كُلِّ شَهْرٍ صِيَامُ اَلدَّهْرِ إِنَّ اَللَّهَ عَزَّ وَ جَلَّ يَقُولُ: «مَنْ جٰاءَ بِالْحَسَنَةِ فَلَهُ عَشْرُ أَمْثٰالِهٰا» »
Commander of the Faithful Imam Ali ibn Abi Talib عليه السلام said: "Fasting the month of patience (Month of Ramadan) and three days of every month removes the anxieties of the chest. Fasting three days in every month is equivalent to fasting for a lifetime. Indeed, Allah سبحانه وتعالى, the Almighty, says: 'Whoever comes with a good deed will have ten times the like of it.'"
- Ṣaḥīḥ al-Faqīh