It is narrated from Sayyiduna Mu'adh bin Anas al-Juhani (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Whoever protects a believer from a hypocrite who backbites him, Allah Almighty will send an angel on the Day of Resurrection to protect his flesh from the fire of Hell. And whoever accuses a Muslim of something, intending thereby to disgrace him, Allah Almighty will detain him on the bridge over Hell until he comes out of what he said."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17568