Narrated Abdullah radiallahu anhu:

The Prophet peace be upon him said "When three persons are together, then no two of them should hold secret counsel excluding the third person."

Two people do not whisper in each other's ears and do not speak secret, some of the members of the assembly do not speak the language that others do not know during the meetings. When two people talk a secret to each other, the third one does not listen between them.

The talk, hiding from a third person and avoiding the broadcasting of him, will hurt that person. The Devil tempts him with lies and distractions. As a result, it hurt a believer, and it is haram to hurt a believer.