Exodus 12:49
47 The whole community of Israel must observe it. 48 “When a resident 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 resident 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.
Numbers 9:14
12 They must not leave any of it until morning, nor break any of its bones; they must observe it in accordance with every statute of the Passover. 13 “‘But the man who is ceremonially clean, and was not on a journey, and fails to keep the Passover, that person must be cut off from his people. Because he did not bring the Lord’s offering at its appointed time, that man must bear his sin. 14 If a resident foreigner lives among you and wants to keep the Passover to the Lord, he must do so according to the statute of the Passover, and according to its custom. You must have the same statute for the resident foreigner and for the one who was born in the land.’” 15 On the day that the tabernacle was set up, the cloud covered the tabernacle—the tent of the testimony—and from evening until morning there was a fiery appearance over the tabernacle. 16 This is the way it used to be continually: The cloud would cover it by day, and there was a fiery appearance by night.
Notes and References
"... the laws imposed on aliens include not only criminal laws but also a number of religious laws as well, and this would seem to be true across all of the pentateuchal sources as defined by critical scholarship ... Resident aliens were in some instances allowed or even required to participate in and benefit from Israelite religious festivals, including the sabbath rest (Exodus 20:10; 23:12; Deuteronomy 5:14), the Day of Atonement - when native-born and resident alien alike were to fast and refrain from work because “atonement is being made for you, to cleanse you” (Leviticus 16:29-30)—and the Passover (as seen in Exodus 12:48-49, where circumcised aliens could participate in Passover, the same law applying to the native-born and the resident alien, and in Numbers 9:14, where a resident alien could celebrate Passover, but only in accordance with the law, the same laws applying to the alien and native-born). The alien was also explicitly allowed to participate in the harvest feasts of Weeks (Deuteronomy 16:11), Tabernacles (Deuteronomy 16:14) and Firstfruits (Deuteronomy 26:11) ..."
Alexander, T. Desmond, and David W. Baker Dictionary of the Old Testament: Pentateuch (p. 30) InterVarsity Press, 2003