Exodus 12:1-4

And Jehovah spake unto Moses and Aaron in the land of Egypt, saying, This month shall be unto you the beginning of months: it shall be the first month of the year to you. Speak ye unto all the congregation of Israel, saying, In 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 be too little for a lamb, then shall he and his neighbor next unto his house take one according to the number of the souls; according to every man’s eating ye shall make your count for the lamb.