Sahih Muslim Book 38, Hadith Number 6691.
Jabir b. Abdullah reported that Allah’s Messenger (may peace be upon him) said: He who climbed this hill, the hill of Murar, his sins would be obliterated as were obliterated the sins of Bani Isra’il. So the first to take their horses were the people of Banu Khazraj. Then there was a ceaseless flow of persons and Allah’s Messenger (may peace be upon him) said to them: All of you are those who have been pardoned except the owner of a red camel. We came to him and said to him: You also come on, so that Allah’s Messenger (may peace be upon him) may seek forgiveness for you. But he said: By Allah, so far as I am concerned, the finding of something lost is dearer to me than seeking of forgiveness for me by your companion (the Holy Prophet), and he remained busy in finding out his lost thing.