Muwatta 1846

Malik transmits from Humayd ibn Qays al-Makki, from Mujahid, that he was with Abdullah ibn Umar when a goldsmith came and said: Abu Abd al-Rahman, I work gold, then sell some of it for more than its weight, and take an extra amount for my labour. Ibn Umar forbade him, and the goldsmith kept repeating it to him while Ibn Umar kept forbidding him, until they reached the door of the mosque. Then Ibn Umar said: dinar for dinar, dirham for dirham, with no excess between them; this is the pledge of our Prophet to us and our pledge to you. ¹

Belongs to the Muwatta, Book of Sales. Source: the Muwatta. Mentions Malik ibn Anas, Humayd ibn Qays al-Makki, Mujahid ibn Jabr, Abdullah ibn Umar ibn al-Khattab. Built on in the chapters on currency exchange (sarf).