Exodus 13:15

13:15 When Pharaoh stubbornly refused to release us, the Lord killed all the firstborn in the land of Egypt, from the firstborn of people to the firstborn of animals. That is why I am sacrificing to the Lord the first male offspring of every womb, but all my firstborn sons I redeem.’

Exodus 16:23

16:23 He said to them, “This is what the Lord has said: ‘Tomorrow is a time of cessation from work, a holy Sabbath to the Lord. Whatever you want to bake, bake today; whatever you want to boil, boil today; whatever is left put aside for yourselves to be kept until morning.’”