Chapter on Obligatory and Recommended Ritual Washing
Tahdhīb al-Aḥkām|Volume 1|Book 1|Chapter 5
وَ بِهَذَا اَلْإِسْنَادِ عَنْ مُحَمَّدِ بْنِ يَعْقُوبَ عَنْ عِدَّةٍ مِنْ أَصْحَابِنَا عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنْ عَلِيِّ بْنِ سَيْفٍ عَنْ أَبِيهِ سَيْفِ بْنِ عَمِيرَةَ عَنِ اَلْحُسَيْنِ بْنِ خَالِدٍ قَالَ: سَأَلْتُ أَبَا اَلْحَسَنِ اَلْأَوَّلَ عَلَيْهِ اَلسَّلاَمُ كَيْفَ صَارَ غُسْلُ يَوْمِ اَلْجُمُعَةِ وَاجِباً قَالَ« إِنَّ اَللَّهَ تَعَالَى أَتَمَّ صَلاَةَ اَلْفَرِيضَةِ بِصَلاَةِ اَلنَّافِلَةِ وَ أَتَمَّ صِيَامَ اَلْفَرِيضَةِ بِصِيَامِ اَلنَّافِلَةِ وَ أَتَمَّ وُضُوءَ اَلنَّافِلَةِ بِغُسْلِ اَلْجُمُعَةِ مَا كَانَ مِنْ ذَلِكَ مِنْ سَهْوٍ أَوْ تَقْصِيرٍ أَوْ نُقْصَانٍ».
Through this chain of narration, from Muhammad ibn Ya’qub, from a group of our companions, from Ahmad ibn Muhammad, from Ali ibn Saif, from his father, Saif ibn Umayrah, from al-Husayn ibn Khalid, who said:
I asked Abu al-Hasan al-Awwal عليه السلام: 'Why is the ghusl of Friday considered obligatory?' Imam عليه السلام said: 'Allah سبحانه وتعالى, completed the obligatory prayer with the supererogatory prayer, completed the obligatory fasting with supererogatory fasting, and completed the ablution for supererogatory acts with the ghusl of Friday to compensate for any oversight, shortcoming, or deficiency in them.'"
- Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 1, p. 116
- Ṣaḥīḥ al-Tahdhīb