2 Samuel 3:23 KJV
When Joab and all the host that was with him were come, they told Joab, saying, Abner the son of Ner came to the king, and he hath sent him away, and he is gone in peace.
The names of those who told Joab that Abner had visited David are not given. But there is no doubt these "they" caused great harm.
I doubt that their intent was to hurt David's reign or hinder the kingdom. They were just the type that likes to gossip and stir up strife. They had a bit of news and they could not keep it in. They knew Joab would be hot. This Abner had killed his brother. It was in battle, and Abner tried to avoid killing him. But Joab held it as a personal grudge.
That was evil enough; but these "they" told Joab, having no interest in it but to see the strife it would cause. What wickedness! What evil! Even if it is not meant to hurt, it is hurtful, wrong and sin.
Years ago a preacher said that one of the most important things he had ever learned was to leave something unsaid every day. The tongue truly is a world of evil and too often we use it to speak things that need not be said or to say things to those who do not need to hear them.
May God help us to bridle our tongues.