The Authority Of Abu Hurairah: The messenger of Allah said : "Do not envy one another; do not inflate prices one to another; do not hate one another; do not turn away from one another; and do not undercut one another, but be you, O servants of Allah, brothers. A muslim is the brother of a muslim: he neither oppresses him nor does he fail him, he neither lies to him nor does he hold him in contempt. Piety is right here-and he pointed to his breast three times. It is evil enough for a man to hold his brother muslim in contempt. The whole of a muslim for another muslim is inviolable: his blood, his property, and his honor."
Related by Muslim.
Hadith Qudsi - Hadith 35