Exodus 12:42
It is a night to be much observed unto the LORD for bringing them out from the land of Egypt: this is that night of the LORD to be observed of all the children of Israel in their generations.
More from Exodus 12
And the LORD 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
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 the house of their fathers, a lamb for an house:
And if the household be too little for the lamb, let him and his neighbour next unto his house take it according to the number of the souls; every man according to his eating shall make your count for the lamb.
Your lamb shall be without blemish, a male of the first year: ye shall take it out from the sheep, or from the goats: