Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 32
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 32, with English translation by Maimonides (Rambam).
לחלוק כבוד לזרעו של אהרן, ולהקדימו לכל דבר שבקדושה, שנאמר: "וְקִדַּשְׁתּוֹ" (ויקרא כא, ח).
To show honor to Aaron's descendants and to give them priority regarding all holy matters, as [Leviticus 21:8] states: "And you shall sanctify him."