The Chapter on Tayammum (Dry Ablution)
Man Lā Yaḥḍuruh al-Faqīh|Volume 1|Book 1|Chapter 22
وَ سَأَلَهُ مُعَاوِيَةُ بْنُ مَيْسَرَةَ: عَنِ اَلرَّجُلِ يَكُونُ فِي اَلسَّفَرِ فَلاَ يَجِدُ اَلْمَاءَ فَيَتَيَمَّمُ وَ يُصَلِّي ثُمَّ يَأْتِي عَلَى اَلْمَاءِ وَ عَلَيْهِ شَيْءٌ مِنَ اَلْوَقْتِ أَ يَمْضِي عَلَى صَلاَتِهِ أَمْ يَتَوَضَّأُ وَ يُعِيدُ اَلصَّلاَةَ قَالَ «يَمْضِي عَلَى صَلاَتِهِ فَإِنَّ رَبَّ اَلْمَاءِ هُوَ رَبُّ اَلتُّرَابِ.
Mu'awiyah ibn Maythara asked Imam Jafar ibn Muhammad Al-Sadiq عليه السلام about a man who is traveling, does not find water, performs tayammum, and prays. Then he finds water while there is still some time left (for the prayer). Should he continue with his prayer or perform wudu and repeat the prayer? Imam عليه السلام said: 'He should continue with his prayer, for the Lord عز وجل of the water is the Lord عز وجل of the earth.'
- Ṣaḥīḥ al-Faqīh, p. 27