Bukhari Collection: ::Book Number 3:: Hadith # 780
Narrated Abu Huraira:The Prophet took a camel of special age from somebody on credit. Its owner came and demanded it back (harshly). The Prophet said, "No doubt, he who has a right, can demand it." Then the Prophet gave him an older camel than his camel and said, "The best amongst you is he who repays his debts in the most handsome way."