Musnad Ahmad 285:2

Waki' narrated to us, he said: Al-A'mash narrated to us, from Abu Wa'il, from Qays ibn Abi Gharzah, who said: We used to buy loads [of produce] in Medina, and we used to be called "the brokers." He said: Then the Messenger of Allah (peace and blessings of Allah be upon him) came to us and named us with a name that was better than what we used to call ourselves. He said: "O assembly of merchants, this selling is attended by idle talk and swearing, so mix it with charity."