how to Detect where user has come from a specific website?

Dear all.
I need help to configure Apache server to handle users requests
using condition based on where he come from so i can redirect him .
what i need if user came with from site start with xn--* redirect him to virtual host
and if he came from any other link then go to another virtual host
please help me with that.
Thanks all,

See original post by hossam mutir