Saeed bin Musayyib (may Allah have mercy on him) says that I heard Sayyiduna Uthman (may Allah be pleased with him) delivering a sermon on the pulpit, saying: I used to buy dates from a Jewish family and tribe called Banu Qaynuqa, and after keeping my profit, I would sell them further. When the Prophet (peace and blessings be upon him) came to know of this, he said: "Uthman! When you buy, weigh it, and when you sell, sell it by weighing."