Musnad Abu Ya'la al-Mawsili 243:64

Ibrahim ibn Sa'id narrated to us, Abu Usamah narrated to us, Burayd ibn 'Abd Allah narrated to us, from Abu Burdah, from Abu Musa, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Allah is more joyful at the repentance of His servant who has transgressed against his own soul than a man who traveled in a desolate, destructive, and ruinous land. When he reached the middle of it, he lost his riding beast. He strove to search for it, going right and left, until he became exhausted or despaired of it, and thought that he would perish. He looked, and found it in a place where he did not expect to find it. Allah, the Almighty and Majestic, is more joyful at the repentance of His transgressing servant than that man was at [finding] his riding beast when he found it."