Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 33
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 33, with English translation by Maimonides (Rambam).
להיות הכהנים לובשים לעבודה בגדי כהונה, שנאמר: "וְעָשִׂיתָ בִגְדֵי קֹדֶשׁ..." (שמות כח, ב).
To clothe the priests with the priestly garments for service [in the Temple], as [Exodus 28:2] states: "And you shall make holy garments...."