"The first day of the week is mentioned in the New Testament only eight times, and is not in a single instance spoken of as a Sabbath, a day of rest, or a sacred day. It is simply called the first day of the week.
On the other hand, inspiration gives the seventh day of the week in the New Testament the sacred title of the Sabbath fifty-nine times.
Mark 16
9 Now when Jesus was risen early the first day of the week,
He appeared first to Mary Magdalene, out of whom He had
cast seven devils."
James White