Chapter on Obligatory and Recommended Ritual Washing
Tahdhīb al-Aḥkām|Volume 1|Book 1|Chapter 5
وَ أَمَّا اَلْخَبَرُ اَلَّذِي رَوَاهُ مُحَمَّدُ بْنُ أَحْمَدَ بْنِ يَحْيَى عَنِ اَلْحُسَيْنِ بْنِ اَلْحَسَنِ اَللُّؤْلُؤِيِّ عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنْ سَعْدِ بْنِ أَبِي خَلَفٍ قَالَ سَمِعْتُ أَبَا عَبْدِ اَللَّهِ عَ يَقُولُ:« اَلْغُسْلُ فِي أَرْبَعَةَ عَشَرَ مَوْطِناً وَاحِدٌ فَرِيضَةٌ وَ اَلْبَاقِي سُنَّةٌ».
As for the narration reported by Muhammad ibn Ahmad ibn Yahya, from al-Husayn ibn al-Hasan al-Lu'lu'i, from Ahmad ibn Muhammad, from Sa’d ibn Abi Khalaf, who said:
I heard Abu Abdullah عليه السلام say: 'There are fourteen occasions for ghusl, one of which is obligatory, and the rest are sunnah.'"
- Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 1, p. 115
- Ṣaḥīḥ al-Tahdhīb