Exodus 13:6
"Seven days thou shalt eat unleavened bread, and in the seventh day shall be a feast to the LORD."
Cross References (ranked by relevance)
Leviticus 23:8
But ye shall offer an offering made by fire unto the LORD seven days: in the seventh day is an holy convocation: ye shall do no servile work therein.
Exodus 34:18
The feast of unleavened bread shalt thou keep. Seven days thou shalt eat unleavened bread, as I commanded thee, in the time of the month Abib: for in the month Abib thou camest out from Egypt.