'First Day' in the Bible

On the first day of the Festival of Unleavened Bread, when the Passover lamb is sacrificed, Jesus' disciples asked him, "Where do you want us to go and make preparations for you to eat the Passover meal?"

Very early on the first day of the week, when the sun had just come up, they were going to the tomb.

After Jesus had risen early on the first day of that week, he appeared first to Mary Magdalene, from whom he had driven out seven demons.