Exodus 12:5

“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.

You shall keep it until the fourteenth day of the same month; and the whole assembly of the congregation of Israel shall kill it at evening.

They shall take some of the blood, and put it on the two door posts and on the lintel, on the houses in which they shall eat it.

They shall eat the meat in that night, roasted with fire, with unleavened bread. They shall eat it with bitter herbs.