What is the ruling on joining the Hizb ut-Tahrir Islamic party and attending their intellectual study circles? Does a Muslim commit a sin if he associates with them? And is masturbation forbidden or permissible?

Hizb ut-Tahrir deviates from the straight path. Among its deviations are: denial of the torment of the grave, reliance on intellect in matters of creed, and abandonment of enjoining good and forbidding evil. They also have uncontrolled fatwas such as: permissibility of shaking hands with and kissing foreign women, the permissibility of paying jizya to a disbelieving state, and the dropping of prayer for a Muslim astronaut. Therefore, it is not permissible to join the party or attend intellectual circles with them.