Leviticus 21:12

ומן המקדש לא יצא NEITHER SHALL HE GO OUT FROM THE SANCTUARY — This means that he must not follow the bier (attend the funeral of his father or mother) (Sanhedrin 18a). Our Rabbis further derived from this (Sanhedrin 84a) the Halacha that the High Priest may perform the sacrificial rites when an “Onan”. The following is how this is implied: even if his father or his mother died he is not required to leave the Sanctuary as may be assumed, but may perform the service; ולא יחלל את מקדש means because he does not thereby (by remaining in the Sanctuary) profane the sacred service, since Scripture permits him to remain and to perform it; it follows therefore that an ordinary priest who officiated when an "Onan" did profane the service (Zevachim 16a; Sanhedrin 84a).

וּמִן־הַמִּקְדָּשׁ֙ לֹ֣א יֵצֵ֔א וְלֹ֣א יְחַלֵּ֔ל אֵ֖ת מִקְדַּ֣שׁ אֱלֹהָ֑יו כִּ֡י נֵ֠זֶר שֶׁ֣מֶן מִשְׁחַ֧ת אֱלֹהָ֛יו עָלָ֖יו אֲנִ֥י יְהֹוָֽה׃

neither shall he go out of the sanctuary, nor profane the sanctuary of his God; for the crown of the anointing oil of his God is upon him: I am the Lord.