'First Day' in the Bible

Now on the first day of the week, Mary Magdalene went early, while it was still dark, to the tomb, and saw the stone taken away from the tomb.

When therefore it was evening, on that day, the first day of the week, and when the doors were locked where the disciples were, for fear of the Jewish leaders, Jesus came and stood in the midst, and said to them, "Peace be to you."