KNOW THAT IT is incumbent on anyone who hears a Muslim being slandered to refute it and to rebuke the speaker. If one cannot restrain him with words, he should restrain him with his hand. If one cannot restrain him with the hand or tongue, one should leave that gathering. If one hears his shaykh, or others who have a right over him, or those who are people of virtue and righteousness, being slandered, one’s concern in this matter should be even greater.
We relate in the book of at-Tirmidhī that Abū ad-Dardā’ 
related that the Messenger of Allah 
said: “Whoever protects the honour of his brother, Allah will protect his face from Hell-Fire on the Day of Rising.” [1].
related that the Messenger of Allah said: “Whoever protects the honour of his brother, Allah will protect his face from Hell-Fire on the Day of Rising.” [1].We relate in the Ṣaḥīḥs of al-Bukhārī and Muslim in the hadith of ‘Itbān—with a kasrah on the ‘ayn in the best known vocalisation, but it has also been cited with a ḍammah— in a long, well-known hadith that he said: “The Prophet stood performing the ṣalāh and then asked: ‘Where is Mālik ibn ad-Dukhshum?’ A man said: ‘That man is a hypocrite; he does not love Allah and His Messenger.’ The Prophet said: ‘Do not say that. Do you not see that he has said “There is no god but Allah”, seeking thereby the Countenance of Allah?’” [2].
in a long, well-known hadith that he said: “The Prophet stood performing the ṣalāh and then asked: ‘Where is Mālik ibn ad-Dukhshum?’ A man said: ‘That man is a hypocrite; he does not love Allah and His Messenger.’ The Prophet said: ‘Do not say that. Do you not see that he has said “There is no god but Allah”, seeking thereby the Countenance of Allah?’” [2].We relate in the Ṣaḥīḥ of Muslim that al-Ḥasan al-Baṣrī, may Allah have mercy on him, reported that ‘Ā’idh ibn ‘Amr, who was one of the Companions of the Messenger of Allah , came to ‘Ubaydullāh ibn Ziyād and said: “O my son, I heard the Messenger of Allah say: ‘The worst shepherds are the harsh ones,’ so beware of being one of them. ‘Ubaydullāh told him: ‘Sit down, for you are of the chaff of the Companions of Muḥammad .’ He said: ‘Was there chaff among them? The chaff was only in those who came after them and others.’” [3].
, came to ‘Ubaydullāh ibn Ziyād and said: “O my son, I heard the Messenger of Allah say: ‘The worst shepherds are the harsh ones,’ so beware of being one of them. ‘Ubaydullāh told him: ‘Sit down, for you are of the chaff of the Companions of Muḥammad .’ He said: ‘Was there chaff among them? The chaff was only in those who came after them and others.’” [3].We relate in the same Ṣaḥīḥs that Ka‘b ibn Mālik said, in his long hadith about the episode of Tabūk: “The Messenger of Allah , while sitting with the people in Tabūk, asked: ‘What has Ka‘b ibn Mālik done?’ A man of the Banū Salimah replied: ‘Messenger of Allah, his two cloaks held him back, and conceit (literally: gazing at his two sides).’ Mu‘ādh ibn Jabal said: ‘What you are saying is reprehensible, by Allah! Messenger of Allah, we know nothing but good of him.’ The Messenger of Allah kept silent.” [4].
said, in his long hadith about the episode of Tabūk: “The Messenger of Allah , while sitting with the people in Tabūk, asked: ‘What has Ka‘b ibn Mālik done?’ A man of the Banū Salimah replied: ‘Messenger of Allah, his two cloaks held him back, and conceit (literally: gazing at his two sides).’ Mu‘ādh ibn Jabal said: ‘What you are saying is reprehensible, by Allah! Messenger of Allah, we know nothing but good of him.’ The Messenger of Allah kept silent.” [4].I say that Salimah is with a kasrah on the lām, and ‘iṭfāhu ‘his two sides’ indicates his self-conceit.
We relate in the Sunan of Abū Dāwūd that Jābir ibn ‘Abdullāh and Abū Ṭalḥah 
related that the Messenger of Allah said: “No man abandons a Muslim man in a place where the reverence due him is violated and his honour diminished but that Allah will abandon him in a situation in which he desires His help. And no man helps a Muslim man in a situation where his honour is being diminished and the reverence due him is being violated without Allah helping him in a situation in which he would like to receive His help.” [5].
related that the Messenger of Allah said: “No man abandons a Muslim man in a place where the reverence due him is violated and his honour diminished but that Allah will abandon him in a situation in which he desires His help. And no man helps a Muslim man in a situation where his honour is being diminished and the reverence due him is being violated without Allah helping him in a situation in which he would like to receive His help.” [5].We relate in [the same source] that Mu‘ādh ibn Anas reported that the Messenger of Allah said: “Whoever protects a believer from a hypocrite. . .” I [Mu‘ādh] believe that he said, “. . .Allah will send an angel to protect his flesh from Hell-Fire on the Day of Rising. Whoever casts an aspersion on a Muslim with something, wishing to disgrace him, Allah will detain him on the Bridge over Hell until he [is able to] emerge from what he said [6]..” [7].
reported that the Messenger of Allah said: “Whoever protects a believer from a hypocrite. . .” I [Mu‘ādh] believe that he said, “. . .Allah will send an angel to protect his flesh from Hell-Fire on the Day of Rising. Whoever casts an aspersion on a Muslim with something, wishing to disgrace him, Allah will detain him on the Bridge over Hell until he [is able to] emerge from what he said [6]..” [7].References
[1] At-Tirmidhī (1932).
[2] Al-Bukhārī (425) and Muslim (33).
[3] Muslim (1830). The implication is that he was not one of the virtuous or one of the scholars among the Companions. Nukhālah, ‘chaff’, is the debris that remains in a sieve after sifting. His reply means that the Companions of the Prophet of Allah were all virtuous, but among those who came after them there was dross.
were all virtuous, but among those who came after them there was dross.[4] Al-Bukhārī (4418) and Muslim (2769).
[5] Abū Dāwūd (4484).
[6] By satisfying the person he disputed with, or by intercession, or by his being punished according to the measure of his wrongdoing.
[7] Abū Dāwūd (4883) and al-Futūḥāt (7/20). Al-Mundhirī alludes to criticism of one of the narrators in the chain of this hadith.