How to determine which control raised an event

[C# Programming]

Hi All,
If I have a form with several buttons and the click event handler for all the buttons points to the same handler, how can I determine in handler which button was clicked?

this.button1.Click += new System.EventHandler(this.button_ClickHandler);
this.button2.Click += new System.EventHandler(this.button_ClickHandler);
this.button3.Click += new System.EventHandler(this.button_ClickHandler);

private void button_ClickHandler(object sender, EventArgs e)
{
MessageBox.Show("Who raised this event?");
}