how to disable postback on gridview with custom dataset

I am a newbee with c# and asp.net.
1- I have a grid view which is with name of GRIDVIEW1
2- GRIDVIEW1 is bound to dataset on PAGELOAD

GridView1.DataSource = dt1;                         GridView1.DataBind();GridView1.DataSource = dt1;
GridView1.DataBind();


3- now i also have a custom Pager, which calls the 
 protected void GridView1_PageIndexChanging(object sender, GridViewPageEventArgs e)
    {
       &nbs ...