Sahih Muslim Book 10, Hadith Number 3900.

Chapter : Prohibition of taking oath in business transactions.

Abu Huraira (Allah be pleased with him) reported: There came a person demanding a camel from Allah’s Messenger (may peace be upon him). He (the Holy Prophet) said: Give him (the camel) of that age or of more mature age, and said: Best among you is one who is best in clearing off the debt.