Albert Barnes Commentary Exodus 12:3

"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:" — Exodus 12:3 (ASV)

A lamb - The Hebrew word is general, meaning either a sheep or a goat—male or female—and of any age; the age and sex are therefore especially defined in the following verse. The direction to select the lamb on the tenth day, the fourth day before it was offered, was intended to ensure due care in the preparation for the great national festival. The custom certainly fell into disuse at a later period, but probably not before the destruction of the temple.