Luke 2:43

and completed the days, and then were returning, the boy Jesus remained behind in Jerusalem, - and his parents noticed it not;

Exodus 12:15

Seven days, unleavened cakes, shall ye eat, surely, on the first day, shall ye put away leaven, out of your houses, - for whosoever eateth what is leavened, then shall that soul be cut off out of Israel, from the first day, unto the seventh day.

2 Chronicles 25:17

Then Amaziah king of Judah took counsel, and sent unto Joash, son of Jehoahaz son of Jehu king of Israel, saying, - Come, let us look one another in the face!

2 Chronicles 30:21-23

And so the sons of Israel who were found in Jerusalem kept the festival of unleavened cakes seven days, with great rejoicing, - and the Levites and the priests, were offering praise unto Yahweh day by day, with loud instruments, unto Yahweh.

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 so the sons of Israel who were found in Jerusalem kept the festival of unleavened cakes seven days, with great rejoicing, - and the Levites and the priests, were offering praise unto Yahweh day by day, with loud instruments, unto Yahweh.
2 Chronicles 25:17
Then Amaziah king of Judah took counsel, and sent unto Joash, son of Jehoahaz son of Jehu king of Israel, saying, - Come, let us look one another in the face!