Lawful Form of Backbiting

"Allah does not like that evil speech should be made public, except by the one who has been oppressed. And Allah is all-Hearing, all-Knowing." Surah An-Nisaa [4:148]

The Following is Evidence from the Sunnah: From 'Aa'ishah (radiAllahu 'anhaa) who said, 'A man was mentioned to the Messenger of Allah (sallAllahu 'alayhi wa salam), so he said, 'How evil a brother he is to the tribe, or a son of the tribe.' So when the man entered, the Prophet spoke kindly with him . I said, 'O Messenger of Allaah, you said what you said, then you spoke kindly with him?' He said, 'O 'Aa'ishah, the most evil of the people is he who abandons the people or the one who gives up on the people fearing their indecency."

From Faatimah Bint Qays (radiAllahu 'anhaa) who said, "The Prophet (sallAllahu 'alayhi wa salam) came so I said, 'Abaa Jahm and Mu'aawiyah have proposed to me.' So the Messenger of Allaah (sallAllahu 'alayhi wa salam) said, 'As for Mu'aawiyah, then he is utterly destitute, not having any wealth. As for Abul-Jahm, then his stick never leaves his back."

Mu'aawiyah was poor and Abul-Jahm used to beat the women. And it is said that the hadeeth means that he used to travel much.

Said Ibn Taymiyyah (d.728H) - rahimahUllah - whilst mentioning that the people it is permissible to rebuke are of various types, and that is not considered backbiting to speak about them, such as the disbeliever, the sinner, the disobedient one, the oppressor, the enticer, the misguided one, and the jealous one...up until he said, "And as for the person, then whatever he possesses of evil can be mentioned in various places."

Then he mentioned from amongst them: the oppressed one can mention what is found with his oppressor and he must mention the proofs concerning that. Then he said, "And from them is that it must be done by way of advising the Muslims concerning their Religion and their worldly life as is found in the authentic hadeeth of Faatimah Bint Qays (radiAllahu 'anhaa).