'First Day' in the Bible

Now on the first day of Unleavened Bread, when they killed the Passover lamb, his disciples said to him, "Where do you want us to go and prepare for you to eat the Passover?"

And very early on the first day of the week, they came to the tomb when the sun had risen.

Now when he rose early on the first day of the week, he appeared first to Mary Magdalene, out of whom he had cast seven demons.