The Prophet ﷺ said, "Whoever defends the honor of his Muslim brother, it becomes binding upon Allah to shield him from the fire of Hell on the Day of Resurrection."
حدثنا إسماعيل عن ليث عن شهر بن حوشب عن أم الدرداء
عن النبي ﷺ قال من رد عن عرض أخيه المسلم كان حقا على الله عز وجل أن يرد عنه نار جهنم يوم القيامة
Its isnad is hasan. Tirmidhi likewise graded it hasan in the Book of Righteousness, 4/327, no. 1931, as did Munziri, 3/51, no. 37. It is also found in Ibn Abu Shayba, 8/388, no. 5591, in the Book of Manners, and in Bayhaqi, 8/168, in the chapter on fighting rebels.