Luke 2:43

and having finished the days, in their returning the child Jesus remained behind in Jerusalem, and Joseph and his mother did not know,

Exodus 12:15

Seven days ye eat unleavened things; only -- in the first day ye cause leaven to cease out of your houses; for any one eating anything fermented from the first day till the seventh day, even that person hath been cut off from Israel.

2 Chronicles 25:17

And Amaziah king of Judah taketh counsel, and sendeth unto Joash son of Jehoahaz, son of Jehu, king of Israel, saying,

2 Chronicles 30:21-23

And the sons of Israel, those found in Jerusalem, make the feast of unleavened things seven days with great joy; and giving praise to Jehovah day by day are the Levites and the priests, with instruments of praise before Jehovah.

Treasury of Scripture Knowledge

Summary

And when they had fulfilled the days, as they returned, the child Jesus tarried behind in Jerusalem; and Joseph and his mother knew not of it.

Bible References

General references

2 Chronicles 30:21
And the sons of Israel, those found in Jerusalem, make the feast of unleavened things seven days with great joy; and giving praise to Jehovah day by day are the Levites and the priests, with instruments of praise before Jehovah.
2 Chronicles 25:17
And Amaziah king of Judah taketh counsel, and sendeth unto Joash son of Jehoahaz, son of Jehu, king of Israel, saying,