after completing farad prayer few people put their right hand on their heads. is it compulsory.? thanks and regards

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.

This act is neither an obligation nor is it legislated, and we are not aware of any evidence of it being legislated, nor have we come across any scholar saying so. Therefore, if someone does it as an act of worship, or habitually does it after each obligatory prayer, then he has done an innovation. The Prophet said: "Whoever introduces into this matter of ours (Islam) that which is not a genuine part of it; it will be rejected.” [Al-Bukhari and Muslim]

Another narration reads: “Whoever performs an act which is not in accordance with ours [our religion], it will be rejected from him.” [Muslim]

Allaah Knows best.