Sahih Muslim Book 10, Hadith Number 3870.

Chapter : He who took something as loan and made its payment back, over and above that (19 approved) and best among you is one who is best in making payment.

Abu Huraira (Allah be pleased with him) reported that Allah’s Messenger (may peace be upon him) deputed a person to collect revenue from Khaibar. He brought fine quality of dates, whereupon Allah’s Messenger (may peace be upon him) said: Are all the dates of Khaibar like this)? He said: No. We got one sa’ (of fine dates) for two sa’s (of inferior dates), and (similarly) two sa’s for three sa’s. Thereupon Allah’s Messenger (may peace be upon him) said: Don’t do that rather sell the inferior quality of dates for dirhams (money), and then buy the superior quality with the help of dirhams.