On the authority of Abu Hurayrah (may Allah be pleased with him) who said:
The Messenger of Allah (peace and blessings of Allah be upon him) said, “Do not envy one another, and do not inflate prices for one another, and do not hate one another, and do not turn away from one another, and do not undercut one another in trade, but [rather] be slaves of Allah and brothers [amongst yourselves]. A Muslim is the brother of a Muslim: he does not oppress him, nor does he fail him, nor does he lie to him, nor does he hold him in contempt. Taqwa (piety) is right here [and he pointed to his chest three times]. It is evil enough for a man to hold his brother Muslim in contempt. The whole of a Muslim is inviolable for another Muslim: his blood, his property, and his honour.”
It was related by Muslim.