Abu Dawud Book 1, Hadith Number 338.
Chapter : A person who is sexually defiled is permitted to eat anything before washing.
Narated By Abu Sa’id al-khudri : Two persons set out on a journey. Meanwhile the time of prayer came and they had no water. They performed tayammum with clean earth and prayed. Later on they found water withen the time of prayer. One of them repeated the prayer and ablution but the other did not repeat. Then they came to the Apostle of Allah (PBUH) and related the matter to him. Addressing himself to the one who did not repeat, he said: You followed the sunnah (model behaviour of the Prophet) and your (first) prayer was enough for you. He said to the one who performed the ablution and repeated: For you there is double reward.
Abu Dawud said: Besides Ibn Nafi’ this is transmitted by al-Laith from ‘Umairah b. Abi Najiyyah from Bakr b. Sawdah on the authority of ‘Ata’ b. Yasar from the Prophet (PBUH).
Abu Dawud said: The mention of (the name of Companion) Abu Sa’id in this tradition is not guarded. This is a mursal tradition (i.e. the Successor ‘Ata’ b. Yasar directly narrates it from the Prophet, leaving the name of the Companions in the chain).