From Sahih Muslim (Hadith 6541):
Abu Huraira reported Allah's Messenger (ﷺ) as saying:Don't nurse grudge and don't bid him out for raising the price and don't nurse aversion or enmity and don't enter into a transaction when the others have entered into that transaction and be as fellow-brothers and servants of Allah. A Muslim is the brother of a Muslim. He neither oppresses him nor humiliates him nor looks down upon him. The piety is here, (and while saying so) he pointed towards his chest thrice. It is a serious evil for a Muslim that he should look down upon his brother Muslim. All things of a Muslim are inviolable for his brother in faith: his blood, his wealth and his honour
Reference: Muslim 6541