"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
2 And very early in the morning, the first day of the week, they came unto the sepulcher at the rising of the sun.
We give this passage, and the following three, because we
are giving every text in the New Testament that mentions the
first day of the week.
---They only show that the first day of the week is called simply the first day of the week."
James White