Sayyidah Asma' bint Yazid (may Allah be pleased with her) said: The Messenger of Allah (peace and blessings be upon him) said: "Whoever defends the honour of his brother in his absence, it is a right upon Allah to protect him from the Fire."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 20813