Musnad Ahmad 1302:24

Isma'il narrated to us, from Layth, from Shahr ibn Hawshab, from Umm al-Darda', from Abu al-Darda', from the Prophet, peace and blessings of Allah be upon him, who said: "Whoever defends the honor of his Muslim brother, it is a right upon Allah, the Almighty and Majestic, to turn away the Fire of Hell from him on the Day of Resurrection."