Sahih Muslim
The Book Pertaining to Repentance and Exhortation to Repentance (Kitab Al-Tauba)
Book Number: 037 / Hadith Number: 6611
Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: Allah is more pleased with the repentance of His servant when he turns penitently towards Him than one of you would be on finding the lost camel.