custom event button.click

Question

would you please tell me what is wrong with this code?

if (button1.Click = true)
{
    this.label1.Text = "custom event";
}

Error is:
the event "...control.click" can only apear on the left hand side of += or -=

I have here a custom event which several buttons can cause.
But in the code I have to know which button caused that custom control.

thank you all