السلام عليكم ورحمة الله وبركاته احس الله إليكم should we reject when someone wants to shake our hands after prayer?

No, but teach him leniently and wisely that it is not the sunnah and the Prophet and the sahabah did the athkar and didn't do this and some of the ulama considered this to be a bid'ah like sheikh Al Islam Ibn Taymiyyah.