It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Do not envy one another, do not hate one another, do not bid up prices against one another (najash), do not turn your backs on one another, and do not sell over the sale of your brother. O servants of Allah, be brothers to one another. A Muslim is the brother of a Muslim: he does not wrong him, nor humiliate him, nor look down upon him. Piety is here," and he (peace and blessings be upon him) pointed to his chest three times. "It is enough evil for a man that he looks down upon his Muslim brother. The blood, honour and wealth of every Muslim are sacred to another Muslim."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب العارية / 11496