I'm triying to devleop a login form, which check username and password from server but when I'm triying to execute code an exception is occured "Connection property is not initialized".

string username = textBox1.Text;
            string pass = textBox2.Text;
            cmd = new SqlCommand("select * from the user_login where username ='" + username + "'", con);
            dr = cmd.ExecuteReader();
            while(dr.Read())
            {
                if((username==dr[0].ToString())&&(pass==dr[1].ToString()))
                {
                    string acc=dr[2].ToString();
                    Class1.access=acc;
                    Form2 mf = new Form2();
                    mf.Show();
                }
                else
                {
                MessageBox.Show("Unauthorized access");
                }
                con.Close();