Zevachim 100 - Does the Mourner Eat the Passover Sacrifice?
Rabbi Shimon made two statements in two different contexts, that the mourner can eat a Passover offering, and that he cannot. The Talmud gives five possible scenarios of how both can be true, one of them being offered by Abaye: one refers to a case when the mourner's relative died before midday, and the other - when he died after midday.
If the relative died before midday when the mourner was not yet fit to offer a Passover sacrifice, then the laws of mourning devolve on him first and prevent him from offering the sacrifice. If, however, the relative died after midday, the mourner was already obligated to bring the Passover sacrifice from before, and then the state of mourning does not prevent him from bringing the sacrifice.
But do we find anywhere a difference between before and after midday? - Yes, we do! There was a story about a kohen named Yosef who did not want to become ritually impure because of his wife's burial, and the other kohanim forced him. On the other hand, the Torah tell the kohanim not to go into the cemetery, with the exception of burying his relatives? We have to say that one ruling applies after midday, while other one - before.
Art: Vasily Perov - Seeing off the Dead