Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 28
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 28, with English translation by Maimonides (Rambam).
לְהַקְטִיר קְטֹרֶת פַּעֲמַיִם בַּיּוֹם, שֶׁנֶּאֱמָר: "וְהִקְטִיר עָלָיו אַהֲרֹן קְטֹרֶת סַמִּים" (שמות ל, ז).
To burn a spice offering twice [each] day, as [Exodus 30:7] states: "And Aaron shall burn incense upon it...."