2 Chronicles 30:3
For they could not keep it at that time, because the priests had not sanctified themselves sufficiently, neither had the people gathered themselves together to Jerusalem.
Cross-reference
2 Chronicles 29:34
Parallel
In 2 Chronicles 29:34, priests also lacked sanctification, causing Levites to help — the same problem as in 30:3.
2 Chronicles 35:6
Parallel
In 2 Chronicles 35:6, Josiah commands priests to sanctify themselves for Passover, echoing the need in 30:3.
Exodus 12:6
Historical context
Exodus 12:6 gives the original Passover date on the 14th of the first month, which they could not keep in 30:3.
Exodus 19:22
Historical context
Exodus 19:22 commands priests to sanctify themselves, which they failed to do in 30:3.