use this code i think it will solve your problem
con.Open();
DateTime dt1, dt2;
DateTime.TryParse(TextBox1.Text, out dt1);
DateTime.TryParse(TextBox2.Text, out dt2);
SqlCommand cmd = new SqlCommand("select company_name,body_model from pur_body where date between '" + dt1 + "' and '" + dt2 + "'", con);
GridView1.DataSource = cmd.ExecuteReader();
GridView1.DataBind();
con.Close();