Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) said: Two men set out on a journey and the time of prayer came while they had no water. Both performed tayammum with clean earth and prayed. Then they found water while the time (of that prayer) still remained. One of them repeated the ablution and the prayer, and the other did not. Then they came to the Messenger of Allah (peace and blessings be upon him) and mentioned the whole incident to him, and he (peace and blessings be upon him) said to the one who had not repeated the prayer: "You have followed the Sunnah, and your prayer was sufficient for you," and he said to the one who had performed ablution and repeated the prayer: "You have a double reward."
Others besides Abdullah bin Nafi' narrated it from al-Layth, from Umayrah bin Abi Najiyah, from Bakr bin Sawadah, from Ata bin Yasar, from the Prophet (peace and blessings be upon him) as mursal.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1094