The Chapter on Tayammum (Dry Ablution)
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 22
وَ سَأَلَ مُحَمَّدُ بْنُ حُمْرَانَ اَلنَّهْدِيُّ وَ جَمِيلُ بْنُ دَرَّاجٍ أَبَا عَبْدِ اَللَّهِ عَلَيْهِ اَلسَّلاَمُ: عَنْ إِمَامِ قَوْمٍ أَصَابَتْهُ جَنَابَةٌ فِي اَلسَّفَرِ وَ لَيْسَ مَعَهُ مِنَ اَلْمَاءِ مَا يَكْفِيهِ لِلْغُسْلِ أَ يَتَوَضَّأُ بَعْضُهُمْ وَ يُصَلِّي بِهِمْ فَقَالَ «لاَ وَ لَكِنْ يَتَيَمَّمُ اَلْجُنُبُ وَ يُصَلِّي بِهِمْ فَإِنَّ اَللَّهَ عَزَّ وَ جَلَّ جَعَلَ اَلتُّرَابَ طَهُوراً كَمَا جَعَلَ اَلْمَاءَ طَهُوراً.
Muhammad ibn Hamran al-Nahdi and Jamil ibn Darraj asked Imam Jafar ibn Muhammad Al-Sadiq عليه السلام about an Imam leading a group in prayer who becomes junub (in a state of major ritual impurity) while traveling and does not have enough water for ghusl (ritual bathing). Should some of them perform wudu and then lead the prayer in his place? Imam عليه السلام said: 'No, rather the junub should perform tayammum and lead them in prayer, for Allah سبحانه وتعالى, the Mighty and Majestic, has made the earth (dust) a means of purification just as He has made water a means of purification.'
- Ṣaḥīḥ al-Faqīh, p. 27