Get text from dynamicly created RichTextBox in onChange event

How can I get the text from a dynamicly created RichTextBox and a dynamicly created rtb_TextChanged Event?

e.g:

    private void button1_Click(object sender, EventArgs e)
    {
        RichTextBox rtb = new RichTextBox();
        rtb.Name = "rtb" + i;
        rtb.Dock = DockStyle.Fill;

        rtb.TextChanged += rtb_TextChanged;

        Controls.Add(rtb);

    }

    void rtb_TextChanged(object sender, EventArgs e)
    {
        //string s = rtb.Text;    //How can I get the rtb.Text?
    }