Abu Hurayrah (may Allah be pleased with him) said that the Prophet (peace and blessings be upon him) said: "Do not envy one another, do not hate one another, do not falsely bid up prices against one another (najsh), do not turn your backs on one another, and do not sell over the sale of one another; and be, O servants of Allah, brothers. A Muslim is the brother of a Muslim: he does not wrong him, does not forsake him and does not look down on him. Piety is here" — and he pointed to his chest three times — and he said: "It is enough evil for a person that he looks down on his Muslim brother. The wealth, life and honour of every Muslim are sacred to the other."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحدود / 17129