Sayyiduna Qays bin Abi Gharazah (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings be upon him) came to us in the market while we were selling slaves in Madinah, and we used to call ourselves 'samasirah', and he (peace and blessings be upon him) gave us a better name than the one we had given ourselves, and said: "O traders, haggling and oaths get mixed into this buying and selling, so mix it with charity."
Hadith Referenceالمعجم الكبير للطبراني / باب القاف / 15997