Exodus 12:1

“This month shall be to you the beginning of months. It shall be the first month of the year to you.

Speak to all the congregation of Israel, saying, ‘On the tenth day of this month, they shall take to them every man a lamb, according to their fathers’ houses, a lamb for a household;

and if the household is too little for a lamb, then he and his neighbor next to his house shall take one according to the number of the souls. You shall make your count for the lamb according to what everyone can eat.