Pesachim 8:2 - 8:3

שחט גדי יאכל – his master [should eat] from him [the kid] and even though all of the other Passover offerings are regular, the frequent is nullified since he didn’t express to him that he relied on it.

יאכל מן הראשון – and the second one should be burned. And in the Gemara (Pesahim 88b) maintains that this is specifically with a king and a queen; there are those who say that it is because of the peace of the kingdom, and there are those who say that because they rely on their servants and they are not exacting about their [Passover] meal, whether with kids or lambs. Therefore, he should eat from the first, since there is no intimation that you care for a thing to be exactly as you want it, for with the first, they have fulfilled their religious obligations. But the people of the world that are particular, he should not either from the first nor the second, for we hold that they are not registered with two Passover offerings as one, to eat from whichever of them that he wants, for there is no retrospective designation. For when he wanted to eat from this one, perhaps at the time of slaughtering, mind was not upon it.

שכח מה שאמר – that he expressed to him a kid or a lamb.

וטלה שלי – In the Gemara (Pesahim 88b) maintains it such as the case where the servant when to the shepherd where his master is accustomed and who wants his remedy (i.e., that things go right for the master), and he (i.e., the shepherd) said to him: “If it is a kid,” your master would tell you that the kid is his and that the lam is your on the condition that your master will not have possession of it,” and in such a manner, the servant acquires itr, for it had not been like this, what the servant acquired, the master acquired and it would be that both of them belong to the master.

ופטורים מלעשות פסח שני – and even though both of them go out to the place of burning and are not eaten because their registration was not known. However, the slaughtering and sprinkling [of the blood] are valid, one for this one and one for the other one, for before Heaven it is revealed.

ON HE WHO ARRIVES IN JERUSALEM FIRST - To encourage them, that they will all try to be first. All children will be on the paschal offering but he who comes first merits first and everyone else does so after him, due to him.

עד שיזרוק הדם – he can take possession, even after the slaughtering until the blood is tossed. But Rabbi Shimon admits that they are not registered other than until it is slaughtered. But the Halakha is not according to Rabbi Shimon.