Ya ayyuha allatheena amanoo itha tanajaytum fala tatanajaw bil-ithmi walAAudwani wamaAAsiyati arrasooli (surah Mujadilah: 9)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(58:9) Believers, when you converse in secrecy, let that not be concerning sin and transgression and disobedience to the Messenger; rather, converse concerning virtue and piety. And fear Allah to Whom all of you shall be mustered. *24

Yaaa ayyuhal lazeena aamanoo izaa tanaajaytum falaa tatanaajaw bil ismi wal `udwaani wa ma`siyatir rasooli wa tanaajaw bil birri wattaqwaa wattaqul laahal lazeee ilaihi tuhsharoon

*24) This shows that najwa (talking secretly together) by itself is not forbidden, but it s being lawful or unlawful depends upon the character of the people who hold secret consultations and upon the circumstances under which such consultations are held, and upon nature of the consultations themselves, If the people whose sincerity, righteousness and purity of character arc well known, arc seen talking secretly together, nobody would have any misgiving that they were planning mischief. On the contrary, the whispering and secret consultations of the people who are notorious for their evil and wicked character, product in every mind. the suspicion that they arc engaged in a new conspiracy. Likewise, if a couple of persons talk for some time together on some matter secretly, it is not objectionable, but if some people have formed themselves into a gang and constantly engaged in a whispering campaign against the Muslim community, this would indeed be a prelude to some mischief. If nothing else, it would at least stir up divisions among the Muslims. Above all, the thing that decides whether najwa (secret counsel) is lawful or unlawful is the nature of the things talked of it. If two men hold a secret counsel in order to bring a dispute the an end, ar to restore a person's right, or to bring a dispute an end, or to restore a person's right, or to promote a good cause, it is no evil, but rather and act of virtue, On the contrary, if the same secret counsel between two men is held with a view to creating mischief, or usurping the rights of . others, or committing a sin, obviously the object itself would be evil and the secret counsel about it evil added w evil.
In this connection, the teaching given by the Holy Prophet (upon whom be Allah's peace) of social etiquette is: "When three men are sitting together, no two of them should whisper to each other, for this would cause anguish to the third. " (Bukhari, Muslim, Musnad Ahmad Thirmidhi Adu Da'ud). In another Hadith, the Holy Prophet said: "Two men should not whisper together, without the leave of the third, for this would cause him anguish. " (Muslim). This objectionable sort of whispering also applies to the cast when two of the three men start talking in a language which is not understood by the third, and even more objectionable would be that during their whispering they should look towards the third person or gesticulate in a manner as to suggest that he is the topic of discussion between them.