Two men set out on a journey and when the time of prayer came they had no water. They preformed tayammum with clean earth and prayed. Later they found water within the time of prayer. One of them repeated the prayer and ablution and the other did not repeat. Then they came to Allah’s Messenger (peace and blessings be upon him) and related the matter to him. Addressing the one who did not repeat, he said: “You followed the sunnah and your prayer was sufficient for you.” He said to the other: “For you there is a double reward.” The double reward may be due to his second prayer or due to his exercising of judgement.

- abu Dawud and al Nasa’i record, on the authority of abu Said al Khudri (may Allah be pleased with him)