“If a Muslim defends his brother’s honor in his absence, Allah will protect his face from the Hell-fire on the Day of Resurrection.”
Related by At-Tirmidhi (1931) and authenticated by Al-Albaani in Saheeh At- Tirmidhi.
The Messenger (sallAllaahu ‘alayhi wasallam) said:
“If a Muslim defends his brother’s honor in his absence…”
Meaning: At the time when his brother isn’t present. So if a person is present in a gathering and his Muslim brother is mentioned therein with a sin that he may have committed or by belittling him then he is supposed to defend him just like he would defend his own honor.
This is because his brother’s honor is equivalent to his honor and thus he must defend it by chastising those backbiters and preventing them from indulging in speaking about his Muslim brother’s honor.
He should not give in and be silent, letting them bad-mouth (his brother). This is an obligation upon (every) Muslim. It is not permissible for him to be mute and submit (to that which they are doing). If he does this, then he falls into sin and consequently