Abdul Malik bin A'yn عبد الملك بن أعين الكوفي مولى بني · Commercial Transactions (Kitab Al-Buyu)

In the time of the Messenger of Allah (ﷺ) we used to be called brokers, but the Prophet (ﷺ) 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).