Chapter on the Description of Ablution (Wudu)
Tahdhīb al-Aḥkām|Volume 1|Book 1|Chapter 4
وَ أَخْبَرَنِي اَلشَّيْخُ أَيَّدَهُ اَللَّهُ تَعَالَى عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنْ أَبِيهِ عَنْ سَعْدِ بْنِ عَبْدِ اَللَّهِ عَنْ أَحْمَدَ بْنِ مُحَمَّدٍ عَنْ أَيُّوبَ بْنِ نُوحٍ قَالَ: كَتَبْتُ إِلَى أَبِي اَلْحَسَنِ عَلَيْهِ اَلسَّلاَمُ أَسْأَلُهُ عَنِ اَلْمَسْحِ عَلَى اَلْقَدَمَيْنِ فَقَالَ« اَلْوُضُوءُ بِالْمَسْحِ وَ لاَ يَجِبُ فِيهِ إِلاَّ ذَلِكَ وَ مَنْ غَسَلَ فَلاَ بَأْسَ».
The Shaykh (Al-Mufid), may Allah سبحانه وتعالى support him, narrated to me from Ahmad bin Muhammad, from his father, from Sa‘d bin Abdullah, from Ahmad bin Muhammad, from Ayyub bin Nuh, who said:
I wrote to Abu Al-Hasan عليه السلام, asking him about wiping over the feet. Imam عليه السلام said: 'Ablution is with wiping, and nothing else is required in it. However, if someone washes [the feet], there is no harm.'"
- Tahdhīb al-Aḥkām fī Sharḥ al-Muqniʿah, vol. 1, p. 67
- Ṣaḥīḥ al-Tahdhīb, p. 52