Pesachim 8:2-3

Pesachim 8:2

If a person directs his servant to offer a Passover sacrifice for him, if the servant offers a kid, the master may eat it. If he offers a lamb, the master may eat it. If he offers both, the master eats from whichever was offered first. If the servant forgot which kind of animal his master told him to offer, he offers both a lamb and a kid saying, “If my master told me to offer a lamb, then the lamb is his and the kid is mine. If he told me to offer a kid, then the kid is his and the lamb is mine.” If the master also forgot what he directed the servant to do, then both animals must be burned (on 16 Nisan); neither the master nor the servant need to bring an offering on second Passover (Pesach sheini, on 14 Iyar).

Pesachim 8:3

If a man tells his sons that he will offer the Passover sacrifice for the first of them to reach Jerusalem (and the others will receive their portions through him), as soon as the first one’s head and the greater part of his body are inside the city walls, he acquires his portion and the others’ on their behalves. Any number of people may divide a Passover offering so long as there is an olive-sized portion for each of them. People may join and leave a group for the offering until it is actually slaughtered; Rabbi Shimon says that one may join or leave the group until the animal’s blood is sprinkled on the altar.