Malik bin Amirah (may Allah be pleased with him) said: Before the Hijrah, the Messenger of Allah (peace and blessings be upon him) bought from me cloth for a pair of trousers for three dirhams. He (peace and blessings be upon him) gave me three dirhams and gave me extra as well.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 11171