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 rejoice if he were riding his mount in a barren wilderness and it slipped away from him, carrying his food and drink. He despairs of finding it, comes to a tree, and lies down in its shade, having given up all hope of his mount. Then, while he is in that state, he suddenly finds it standing beside him. He grabs its rein and, in the intensity of his joy, exclaims, 'O Allah, You are my servant, and I am Your Lord!' He misspeaks out of the 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 chapter on repentance (2747) through several routes from Umar bin Yunus, who said, Ikrima bin Ammar told us, Ishaq bin Abdullah bin Abu Talha told us, Anas bin Malik, who was his uncle, told us, and he related it.There are other hadiths on this same subject, and they are mentioned in their proper place.