The Messenger of Allah ﷺ said, "Allah rejoices more at the repentance of His servant when he turns to Him in Tawba than any of you would over his mount that escaped from him in a desert land, carrying his food and drink. After he had given up hope of finding it, he came to a tree and lay down in its shade, despairing of his mount. While he was in that state, suddenly there it was, standing beside him. He seized its halter and, in the intensity of his joy, said, 'O Allah, You are my servant and I am Your Lord!' He misspoke from the sheer intensity of his joy."
قال رسول الله ﷺ: الله أشد فرحا بتوبة عبده حين يتوب إليه من أحدكم كان على راحلته بأرض فلاة، فانفلتت منه وعليها طعامه وشرابه، فأيس منها، فأتى شجرة، فاضطجع في ظلها، قد أيس من راحلته، فبينا هو كذلك إذا هو بها قائمة عنده، فأخذ بخطامها، ثم قال من شدة الفرح: اللهم أنت عبدي وأنا ربك، أخطأ من شدة الفرح.
Muslim narrated it in the Book of Repentance (2747) through several routes from Umar bin Yunus, who said, Ikrima bin Ammar told us, who said, Ishaq bin Abdullah bin Abu Talha told us, who said, Anas bin Malik told us, and he related it.