The Feast of the Passover: Strangers and Servants when Circumcised Might Keep
Source: TTT
Exodus 12:44, 48
But any slave who has been purchased may eat of it, after you have circumcised him. / If a foreigner resides with you and wants to celebrate the LORD’s Passover, all the males in the household must be circumcised; then he may come near to celebrate it, and he shall be like a native of the land. But no uncircumcised man may eat of it.