Halakha Imamat 16:2: Mishneh Torah, Negative Mitzvot & Sefer HaChinukh

Not to allow the Sanctuary to remain unwatched, as it is said, “And ye shall keep the charge of the Sanctuary” (Num. 18:5).

That the priest shall not enter the Sanctuary at all times^*But only when he is to perform service there., as it is said, “(Speak to Aaron thy brother) that he come not at all times into the holy place” (Lev. 16:2).

That the priests not enter at any time into the Temple — and all the more so, non-priests: That the priests not enter at any time into the Temple, but rather only at the time of the service, as it is stated (Leviticus 16:2), “and let him not come at any time.” And with this, the high priest is warned not to come into the house of the Holy of Holies — and even on Yom Kippur — except at the time of the service. [And likewise brought into (this) warning is a common priest from entering the sanctuary all of the year except at the time of the service (according to the Venice edition)]. And the elucidation of the matter of the prevention is to say that any priest not enter into any place that is fitting, except at the time that is fitting to enter it — which is the time of service. And the language of Sifra, Acharei Mot, Section 1:8, 10 is “‘And let him not come at any time’ — that is Yom Kippur; ‘to the holy’ — to include the other days of the year. ‘Within the partition’ — maybe for all of the sanctuary, [the punishment is] death. [Hence] we learn to say, ‘before the ark cover which is on the ark, that he not die.’ Behold, how is this? ‘Before the ark cover’ [is punishable] by death; (if he enters) the other parts of the sanctuary, (he is only in transgression of) a warning. And in the Gemara Menachot 27b, they, may their memory be blessed, said, about the chamber that it is with forty [lashes].