4,003. Substitute Kohanim

Hilchos Bias HaMikdash 4:13

If the korban Pesach (Passover sacrifice) is offered in impurity and those who were ritually unclean with corpse impurity entered the Heichal (the Sanctuary), they are exempt. This is so even though they were only permitted to enter the courtyard because Numbers 5:3 – “Send them out from the camp” – doesn’t apply to them.

Hilchos Bias HaMikdash 4:14

If part of the priestly family assigned to serve in the Temple on a given day were ritually unclean, while others were clean, only those who are clean may perform the service. This is so even if the majority are ritually unclean with corpse impurity. If all the members of that priestly family are unclean, a different priestly family is brought in to serve. If all the kohanim of that watch are unclean with corpse impurity, another watch is sought. If most of the kohanim in Jerusalem at the time are unclean, sacrifices are offered in ritual impurity.