The Lord said to Moses and Aaron in the land of Egypt:
References for Exodus 12:1
"This month is to be the beginning of months for you; it is the first month of your year.
Tell the whole community of Israel that on the tenth day of this month they must each select an animal of the flock according to [their] fathers' households, one animal per household.
If the household is too small for a [whole] animal, that person and the neighbor nearest his house are to select one based on the combined number of people; you should apportion the animal according to what each person will eat.
References for Exodus 12:4
You must have an unblemished animal, a year-old male; you may take it from either the sheep or the goats.
You are to keep it until the fourteenth day of this month; then the whole assembly of the community of Israel will slaughter the animals at twilight.