'First Day' in the Bible

So on the first day of the seventh month, Ezra the priest brought out the Law before the assembled people. Both men and women were in attendance, as well as all who could understand what they were hearing.

and Ezra continued to read from the Book of the Law of God day by day, from the first day through the last. They celebrated for seven days, and on the eighth day they held a solemn assembly according to regulation.