Exodus 12:43-51 - Institution Of The Passover
43 The Lord said to Moses and Aaron, "This is the ordinance of the Passover. No foreigner may share in eating it. 44 But everyone's servant who is bought for money, after you have circumcised him, may eat it. 45 A foreigner and a hired worker must not eat it. 46 It must be eaten in one house; you must not bring any of the meat outside the house, and you must not break a bone of it. 47 The whole community of Israel must observe it. 48 "When a foreigner lives with you and wants to observe the Passover to the Lord, all his males must be circumcised, and then he may approach and observe it, and he will be like one who is born in the land -- but no uncircumcised person may eat of it. 49 The same law will apply to the person who is native-born and to the foreigner who lives among you."
50 So all the Israelites did exactly as the Lord commanded Moses and Aaron. 51 And on this very day the Lord brought the Israelites out of the land of Egypt by their regiments.