Sayyiduna Wathilah bin al-Asqa' (may Allah be pleased with him) says that he heard the Messenger of Allah (peace and blessings be upon him) say: "The blood, honour and wealth of a Muslim are sacred (haram) for another Muslim. A Muslim is the brother of a Muslim; he does not wrong him, nor does he forsake him. Taqwa (God-consciousness) is here," and he (peace and blessings be upon him) pointed with his hand towards the heart, "and it is enough evil for a person that he looks down on his Muslim brother."
Hadith Referenceالمعجم الكبير للطبراني / باب الواو / 18403