Musnad Abu Ya'la al-Mawsili 115:19

Hadaba narrated to us, Hammam narrated to us, Qatada narrated to us, from Anas, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Allah is more joyful at the repentance of His servant than one of you who wakes up to find his camel, which he had lost, in a desolate wasteland."