Ezra 6:20-21

20 For the priests and the Levites had purified themselves together; all of them were clean. So they killed the passover lamb for all the returned exiles, for their fellow priests, and for themselves;
21 it was eaten by the people of Israel who had returned from exile, and also by every one who had joined them and separated himself from the pollutions of the peoples of the land to worship the LORD, the God of Israel.