Exodus 12:48

48 aIf a stranger shall sojourn with you and would keep the Passover to the Lord, let all his males be circumcised. Then he may come near and keep it; he bshall be as a native of the land. But no uncircumcised person shall eat of it.

Numbers 9:5

5And they kept the Passover in the first month, on the fourteenth day of the month, at twilight, in the wilderness of Sinai; according to all that the Lord commanded Moses, so the people of Israel did.
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