In the Hagadah (page 8 of here), there is a line by the wicked son that says you should "remove his teeth" (hakeih et shinav). A common explanation is that the gematria of "rasha" (reish shin ein: 570) minus "his teeth"(shin nun yud vav: 366) equals "tzadik"(tzadi daled yud kuf: 204). What is the earliest use of this gematria to explain that line?
The אגישמקע וורט on the Haggadah writes that both the Alshich and the Arugas HaBosem say this vort.
And I saw in one of the commentaries that the explanation of this vort is that when it says in the Haggadah to blunt the teeth of the wicked son, it means to you should endeavor to remove from him his wickedness so that he becomes a Tzaddik.