Chapter on Virtues of Hajj
Man Lā Yaḥḍuruh al-Faqīh|Volume 2|Book 3|Chapter 2
وَ رُوِيَ عَنْ مُوسَى بْنِ جَعْفَرٍ عَلَيْهِمَا اَلسَّلاَمُ أَنَّهُ قَالَ: «فِي خَمْسَةٍ وَ عِشْرِينَ مِنْ ذِي اَلْقَعْدَةِ أَنْزَلَ اَللَّهُ عَزَّ وَ جَلَّ اَلْكَعْبَةَ اَلْبَيْتَ اَلْحَرَامَ فَمَنْ صَامَ ذَلِكَ اَلْيَوْمَ كَانَ كَفَّارَةَ سَبْعِينَ سَنَةً وَ هُوَ أَوَّلُ يَوْمٍ أُنْزِلَتْ فِيهِ اَلرَّحْمَةُ مِنَ اَلسَّمَاءِ عَلَى آدَمَ عَلَيْهِ اَلسَّلاَمُ ».
It has been narrated from Imam Musa ibn Jafar Al-Kadhim عليه السلام that he said: "On the 25th of Dhu al-Qa'dah, Allah سبحانه وتعالى, the Mighty and Majestic, sent down the Kaaba, the Sacred House. Whoever fasts on that day will have the expiation of seventy years of sins. It is also the first day on which mercy was sent down from the heavens upon Adam عليه السلام."
- Ṣaḥīḥ al-Faqīh