Musnad Ahmad 1302:31

Ali ibn Ishaq narrated to us, Abdullah—meaning Ibn al-Mubarak—informed us, he said: Abu Bakr al-Nahshali informed us, from Marzuq Abu Bakr al-Taymi, from Umm al-Darda, from Abu al-Darda, from the Prophet, may God bless him and grant him peace, who said: "Whoever defends the honor of his brother, God will defend his face from the Fire on the Day of Resurrection."