asalamu alaikum is it haraam to record some one's conversation without the person knowing that they are being recorded?in this conversation some personal things were said.also this person was attepmting to use this recording as a means to use is agianst the other person that was talking.is this act haraam? please reply quickly.thank you!

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 is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

It is not permissible to record someone's conversation without his knowledge and permission, as this act includes some religious prohibitions among which are:

1-     Spying, and this is forbidden. Allaah Says (what means): {....And spy not}[Quran 49: 12].

2-     Listening to his conversation without his knowledge, and it is sure that he dislikes being listened to in this way. The Prophet said: "Whoever listens to the talk of some people who do not like (to be heard) or they run away from him (lest he hears them), then molten lead will be poured into his ears on the Day of Resurrection."  For more benefit, please refer to Fatwa 83404.

Therefore, it is not permissible to record his conversation, and the fact that it is going to be used against him does not make it permissible. This is of course if recording this conversation is not a way of obtaining a preponderant benefit, like getting back one's right and the like, as in this case it is permissible to record his conversation in the manner described in the question.

Allaah Knows best.