It is narrated from Hazrat Abu Darda (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "Whoever defends the honor of his Muslim brother, it is incumbent upon Allah to free him from the fire of Hell on the Day of Resurrection."
Hadith Referenceمسند احمد / من مسند القبائل / 27609
Hadith Gradingحکم دارالسلام:إسناده ضعيف لضعف عبيدالله بن أبى زياد، وشهر بن حوشب