'First Day' in the Bible

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.

And on the first day ye shall have a holy convocation, and on the seventh day a holy convocation: no manner of work shall be done on them, save what is eaten by every person that only shall be done by you.