You did use rounge procedure for getting value of hiddefield with in repeater
in simple way I provide you :-
<input type="hidden" id="Rizwan" value='<%# Eval("user_id") %>' />
AND YOUR CODE BEHIND :-
HiddenField hd = (HiddenField)e.Item.FindControl("Rizwan");
I hope your Problem will resolve if not Please give me your Comment.