Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 24

לְקַדַּשׁ הַכּוֹהֵן יָדָיו וְרַגְלָיו בְּשָׁעַת הָעֲבוֹדָה, שֶׁנֶּאֱמָר: "וְרָחֲצוּ אַהֲרֹן וּבָנָיו..." (שמות ל, יט).

For a priest to sanctify his hands and feet at the time of service [in the Temple], as [Exodus 30:19] states: "And Aaron and his sons will wash...."