'First Day' in the Bible

And on the first day of the feast of unleavened bread, when they sacrificed the paschal lamb, his disciples said to Him, Where wouldst thou have us go and make preparation for thee to eat of the paschal lamb?

and very early in the morning of the first day of the week they come to the sepulchre at sun-rising.

Now Jesus being risen early on the first day of the week appeared first to Mary Magdalene, from whom He had cast out seven devils: