Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 59
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 59, with English translation by Maimonides (Rambam).
לתקוע בחצוצרות על הקרבנות ובשעת הצרות, שנאמר: "וּתְקַעְתֶּם בַּחֲצוֹצְרֹת" (במדבר י, י).
To sound the trumpets when the sacrifices [are offered] and in times of difficulty, as [Numbers 10:10] states: "And you shall sound the trumpets...."