Al-Kāfi

Hadith 576
fasting
2ـ عِدَّةٌ مِنْ أَصْحَابِنَا عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنِ الْحَسَنِ بْنِ مَحْبُوبٍ عَنْ إِبْرَاهِيمَ بْنِ مِهْزَمٍ عَنْ حُسَيْنِ بْنِ أَبِي حَمْزَةَ عَنْ أَبِي حَمْزَةَ قَالَ قُلْتُ لأَبِي جَعْفَرٍ (عَلَيْهِ السَّلاَم) صَوْمُ ثَلاثَةِ أَيَّامٍ مِنْ كُلِّ شَهْرٍ أُؤَخِّرُهُ إِلَى الشِّتَاءِ ثُمَّ أَصُومُهَا قَالَ لا بَأْسَ بِذَلِكَ.
2. A number of our people have narrated from Ahmad ibn Muhammad from al-Hassan ibn Mahbub from Ibrahim ibn Mahziyar from Husayn ibn abu Hamzah who has said the following: “I once asked abu Ja‘far (a.s.), if I can delay fasting of three days of every month to fast in winter. He (the Imam) said, ‘It is not harmful.’”
Source: Shaykh Muḥammad b. Yaʿqūb al-Kulaynī