The Messenger of Allah ﷺ forbade muzabanah, muhaqalah, and making an exception in a sale unless what is excepted is clearly known.
حدثنا أبو حفص عمر بن يزيد السياري حدثنا عباد بن العوام عن سفيان بن حسين عن يونس بن عبيد عن عطاء
نهى رسول الله ﷺ عن المزابنة والمحاقلة وعن الثنيا إلا أن يعلم
[Its isnad is hasan] Tirmidhi reported it, Chapter on Business Transactions, section on what has been said regarding the prohibition of thunya, hadith no. 1290, from the hadith of Abbad bin Awwam, with this wording, and he said, hasan sahih ghareeb. Nasai also reported it, hadith no. 4637.