Exodus 12:5-7

5The animals you choose must be year-old males without defect, and you may take them from the sheep or the goats. 6Take care of them until the fourteenth day of the month, when all the members of the community of Israel must slaughter them at twilight. 7Then they are to take some of the blood and put it on the sides and tops of the doorframes of the houses where they eat the lambs.