Luke 2:43

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.

Cross References

Exodus 12:15 Seven days shall ye eat unleavened bread; even the first day ye shall put away leaven out of your houses: for whosoever eateth leavened bread from the first day until the seventh day, that soul shall be cut off from Israel.
2 Chronicles 25:17 Then Amaziah king of Judah took advice, and sent to Joash, the son of Jehoahaz, the son of Jehu, king of Israel, saying, Come, let us see one another in the face.
2 Chronicles 30:21-23 And the children of Israel that were present at Jerusalem kept the feast of unleavened bread seven days with great gladness: and the Levites and the priests praised the LORD day by day, singing with loud instruments unto the LORD. And Hezekiah spake comfortably unto all the Levites that taught the good knowledge of the LORD: and they did eat throughout the feast seven days, offering peace offerings, and making confession to the LORD God of their fathers. And the whole assembly took counsel to keep other seven days: and they kept other seven days with gladness.