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 (ranked by relevance)
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.