'First Day' in the Bible

that I may build a house for the name of the LORD my God, to consecrate it to him to burn sweet odours and to set shewbread before him perpetually, and for burnt sacrifices morning and evening, and on the Sabbath days, and the first day of every new moon, and in the solemn feasts of the LORD our God, so to continue ever in Israel.

Now they began on the first day of the first month to sanctify, and on the eighth day of the month came they to the porch of Jehovah; and they sanctified the house of Jehovah in eight days: and on the sixteenth day of the first month they made an end.