The Sufficient (Vol 4) · Hadith 345 (#Ḥadīth #7)
Chapter 13 | Excellence of Fasting in the Month of Shaman, Continuing Such Fast to Connect it with the Month of Ramadan, and Three Days of Fasting Every Month
7ـ عِدَّةٌ مِنْ أَصْحَابِنَا عَنْ سَهْلِ بْنِ زِيَادٍ عَنْ أَحْمَدَ بْنِ مُحَمَّدِ بْنِ أَبِي نَصْرٍ قَالَ سَأَلْتُ أَبَا الْحَسَنِ (عَلَيْهِ السَّلاَم) عَنِ الصِّيَامِ فِي الشَّهْرِ كَيْفَ هُوَ قَالَ ثَلاثٌ فِي الشَّهْرِ فِي كُلِّ عَشْرٍ يَوْمٌ إِنَّ الله تَبَارَكَ وَتَعَالَى يَقُولُ مَنْ جاءَ بِالْحَسَنَةِ فَلَهُ عَشْرُ أَمْثالِها ثَلاثَةُ أَيَّامٍ فِي الشَّهْرِ صَوْمُ الدَّهْرِ.
7. A number of our people have narrated from Sahl ibn Ziyad from Ahmad ibn Muhammad ibn abu Nasr who has said the following: “I asked abu al-Hassan , about fasting during a month. He replied, ’It is three days every month, one day in every ten days. Allah, the most Blessed, the most High, says, “One who does a good deed receives tenfold reward.” (6:151) Three days of fasting every month is like fasting all the time.’”
Gradings are classical jarḥ-wa-taʿdīl, name-matched to a rijāl index (not individually re-verified).