Hajjaj bin al-Minhal حجاج بن المنهال · The Chapters on Business Transactions

"May Allah have mercy on a person who is lenient when he sells, lenient when he buys, and lenient when he asks for payment. "

"Makhrafah Al' Abdi and I brought linens from Hajar The Messenger of Allah (ﷺ) came to us to bargain with us with some trousers. There was someone with me who weighed (the goods) in exchange for a wage. So the Prophet (ﷺ) said to the one weighing: 'Weigh and add more.'"