Luke 2:43

and had completed the days, as they returned, the boy Jesus remained behind in Jerusalem, and his parents knew not of it;

Exodus 12:15

Seven days shall ye eat unleavened bread: on the very first day ye shall put away leaven out of your houses; for whoever eateth leavened bread from the first day until the seventh day that soul shall be cut off from Israel.

2 Chronicles 25:17

And Amaziah king of Judah took counsel, and sent to Joash the son of Jehoahaz, the son of Jehu, king of Israel, saying, Come, let us look one another in the face.

2 Chronicles 30:21-23

And the children of Israel, that were present at Jerusalem, held the feast of unleavened bread seven days with great gladness; and the Levites and the priests praised Jehovah day by day, with the instruments of praise to 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 children of Israel, that were present at Jerusalem, held the feast of unleavened bread seven days with great gladness; and the Levites and the priests praised Jehovah day by day, with the instruments of praise to Jehovah.
2 Chronicles 25:17
And Amaziah king of Judah took counsel, and sent to Joash the son of Jehoahaz, the son of Jehu, king of Israel, saying, Come, let us look one another in the face.