Anas (may Allah be pleased with him) narrates from the Prophet (peace and blessings of Allah be upon him), he said: "If someone backbites his Muslim brother in his presence and he is able to support and defend him, and he does so, then Allah will support and defend him in this world and the Hereafter. But if he does not support him despite being able to do so, then Allah will leave him without help in this world and the Hereafter." Weak, even fabricated. Narrated in Sharh al-Sunnah.