Musnad Ahmad 30:1073

The Messenger of Allah, may Allah bless him and grant him peace, said: "Would any of you rejoice over his riding beast if it were lost from him, and then he found it?" They said: "Yes, O Messenger of Allah." He said: "By the One in Whose hand is the soul of Muhammad, Allah is more joyful at the repentance of His servant when he repents than any one of you is over his riding beast when he finds it."