TSK · Numbers 9:3

and you shall keep it until the fourteenth day of the same month; and the whole assembly of the congregation of Israel shall kill it at evening.

In the second month, on the fourteenth day at evening they shall keep it; they shall eat it with unleavened bread and bitter herbs.

Then they killed the Passover on the fourteenth [day] of the second month: and the priests and the Levites were ashamed, and sanctified themselves, and brought burnt offerings into the house of Yahweh.