Pesachim 8:8-9:1

Pesachim 8:8

An onen (one who lost a close relative that day) immerses in a mikvah and eats his Passover offering after nightfall but he does not partake of other sacrifices. One who learns of a relative’s passing or who gathers a parent’s remains for re-interment can immerse in a mikvah and eat other sacrifices. If a non-Jew converts to Judaism on 14 Nisan, Beis Shammai say that he immerses in a mikvah and eats the Passover offering that night. Beis Hillel say that being circumcised is comparable to corpse uncleanliness (and therefore the convert will be unclean for a week and cannot eat the Passover offering that night).

Pesachim 9:1

If a person was ritually unclean or away from Jerusalem on a trip with the result that he could not bring the Passover offering on 14 Nisan, he must observe second Passover (Pesach sheini). If he did not bring the Passover offering because he made a mistake regarding the date or was prevented by circumstances beyond his control, he must observe Pesach sheini. If all of these people must observe Pesach sheini, why does the Torah only mention those who are unclean and those who are out of town? The ones mentioned by the Torah are not liable for kareis (excision) if they skip Pesach sheini but the others would be liable to kareis in such a case.