Whoever Defends His Brother's Honor…

The Prophet (peace and blessings of ALLAH be upon him) said:
"Whoever defends his brother's honour, ALLAH will protect his face from the Fire of the Day of Resurrection."

Reference:
[Narrated and classed as Hasan by al-Tirmidhi. Classed as Hasan by al-Albani, Ghayah al-Maram (below Hadith 431).]