Abu Dawud Book 16, Hadith Number 3320.

Narated By Qays ibn AbuGharazah : In the time of the Apostle of Allah (PBUH) we used to be called brokers, but the Prophet (PBUH) came upon us one day, and called us by a better name than that, saying: O company of merchants, unprofitable speech and swearing takes place in business dealings, so mix it with sadaqah (alms).