Assalamu 'alaikum.I understand that backbiting is a heinous crime and we should all seek refuge in Allah from doing such an act. However, I wanted to know if, for instance, person A backbites (meaning he says something negative) about person B to me. Now every time I think about this negative thought in my head about person B, does this mean Person A will get sins for every such instance i.e. every time this thought appears in my mind?Jezak Allah khair

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger. 

If one person backbites another while you are listening, then you must forbid him from backbiting; otherwise, you would share the sin with him. If you did not forbid him while you were able to do so, then you must sincerely repent from that sin. The backbiter is obliged to repent of his sin and regret his evil deed. Many of the scholars held that the backbiter is obliged to seek the forgiveness and pardon of the person whom he has backbitten (so as to clear himself of liability). Other scholars held that the backbiter is not obliged to seek the pardon of the person whom he has backbitten and it is sufficient for him to ask Allaah for forgiveness for that person and speak well of him. This was the opinion chosen by Shaykhul-Islam Ibn Taymiyyah and it eliminates the evil and reduces the potential harm that may result from informing a person that he has been backbitten. For more benefit, please refer to Fataawa 89880 and 92219.

As for the inquiry regarding whether the backbiter's sin increases whenever you remember the negative words uttered by him, we know of no religious evidence supporting that and we could not find any statement by the scholars to that effect.

Allaah Knows best.