The Chapter on Tayammum (Dry Ablution)
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 22
وَقَالَ زُرَارَةُ وَ مُحَمَّدُ بْنُ مُسْلِمٍ: قُلْنَا لِأَبِي جَعْفَرٍ عَلَيْهِ اَلسَّلاَمُ رَجُلٌ لَمْ يُصِبْ مَاءً وَ حَضَرَتِ اَلصَّلاَةُ فَتَيَمَّمَ وَ صَلَّى رَكْعَتَيْنِ ثُمَّ أَصَابَ اَلْمَاءَ أَ يَنْقُضُ اَلرَّكْعَتَيْنِ أَوْ يَقْطَعُهُمَا وَ يَتَوَضَّأُ ثُمَّ يُصَلِّي قَالَ «لاَ وَ لَكِنَّهُ يَمْضِي فِي صَلاَتِهِ فَيُتِمُّهَا وَ لاَ يَنْقُضُهَا لِمَكَانِ اَلْمَاءِ لِأَنَّهُ دَخَلَهَا وَ هُوَ عَلَى طُهْرٍ بِتَيَمُّمٍ» وَقَالَ زُرَارَةُ قُلْتُ لَهُ دَخَلَهَا وَ هُوَ مُتَيَمِّمٌ فَصَلَّى رَكْعَةً ثُمَّ أَحْدَثَ فَأَصَابَ مَاءً قَالَ «يَخْرُجُ فَيَتَوَضَّأُ ثُمَّ يَبْنِي عَلَى مَا مَضَى مِنْ صَلاَتِهِ اَلَّتِي صَلَّى بِالتَّيَمُّمِ.
Zurarah and Muhammad ibn Muslim said: We asked Abu Ja'far عليه السلام about a man who does not find water, and the time for prayer arrives, so he performs tayammum and prays two rak'ahs. Then he finds water. Should he invalidate the two rak'ahs, does he interrupt them, perform wudu, and then repeat the prayer? Imam عليه السلام said: 'No, he should continue his prayer and complete it, and the presence of water does not invalidate it because he entered into it while in a state of purity through tayammum.' Zurarah also said: I asked him about a person who entered the prayer with tayammum, prayed one rak'ah, then broke his wudu and now has also found water. Imam عليه السلام said: 'He should go out, perform wudu, and then continue from where he left off in the prayer that he began with tayammum.'
- Ṣaḥīḥ al-Faqīh, p. 26