Sahih al-Bukhari Book 34, Hadith 32
Allah's Messenger (ﷺ) said, "The seller and the buyer have the right to keep or return goods as long as they
have not parted or till they part; and if both the parties spoke the truth and described the defects and
qualities (of the goods), then they would be blessed in their transaction, and if they told lies or hid
something, then the blessings of their transaction would be lost."
The Prophet (ﷺ) said, "There was a merchant who used to lend the people, and whenever his debtor was in straitened circumstances, he would say to his employees, 'Forgive him so that Allah may forgive us.' So, Allah forgave him."
We used to be given mixed dates (from the booty) and used to sell (barter) two Sas of those dates) for one Sa (of good dates). The Prophet (ﷺ) said (to us), "No (bartering of) two Sas for one Sa nor two Dirhams for one Dirham is permissible", (as that is a kind of usury). (See Hadith No. 405).