Exodus 12:3-11 is the original Passover institution that Josiah commands to follow 'as it is written', making this a direct citation.

Leviticus 23:5-8 lists the Passover and Unleavened Bread as appointed feasts—the very law Josiah commands them to observe.

Numbers 9:2-5 gives specific instructions for keeping Passover, including for the unclean—the law Josiah is enforcing.

Numbers 28:16-25 details the offerings required for Passover and Unleavened Bread—the ritual Josiah reinstitutes.

Deuteronomy 16:1-8 is the Passover law from the Book of the Covenant Josiah found—he commands exactly this.

2 Chronicles 35:1-19 provides the full account of the Passover Josiah commanded, expanding on the brief mention here.

Exodus 12:14 institutes the Passover as a perpetual memorial—the very command Josiah now orders the people to keep.

Exodus 12:21 records Moses telling elders to select the Passover lamb—the origin of the practice Josiah revives.

Exodus 23:15 commands the Feast of Unleavened Bread at the appointed time—the same festival Josiah observes.

2 Chronicles 34:30 records Josiah reading the covenant before the people—the context for his Passover command.

2 Chronicles 35:18 describes the unique Passover Josiah kept—the same event commanded in Kings.