The 76th prohibition is that a kohen who is a t'vul yom1 — even if he has purified himself — is forbidden from serving in the Temple until the sun has set.

The source of this prohibition is G‑d's statement2 (exalted be He), regarding the kohanim, "[They must be holy to their G‑d] and they must not profane their G‑d's Name."

One who transgresses this prohibition by serving in the Temple while a t'vul yom is punished by misah biy'dei shamayim.

This is not explicitly stated in Scripture, but has been passed down by the Oral Tradition. In the ninth chapter of Sanhedrin3 our Sages clearly said that this is the meaning of G‑d's statement (exalted be He), "They must be holy to their G‑d and they must not profane (v'lo y'chal'luhu) their G‑d's Name." They said: "It cannot teach us the prohibition of one who is tameh [serving in the Temple], because it has already been given. If so, this verse must teach us the prohibition of a t'vul yom serving [in the Temple]. And we learn from the usage of the word chillul [that the penalty is misah biy'dei shamayim4]." This prohibition is included there among the list of those who are punishable by death.