Numbers 9:10-11

10‘Say to the Israelites, “Anyone among you or your descendants may become not clean because of a dead body. Or they may be away because they are travelling. They can still eat the Passover meal to thank the Lord.

11They must eat it during the evening of the 14th day of the second month. They must eat it when it starts to become dark. They must eat it with bread and with bitter herbs. The bread must not have yeast in it.