Mishneh Torah — Positive Mitzvot מצוות עשה, Chapter 170
The full Hebrew text of Mishneh Torah, Positive Mitzvot, Chapter 170, with English translation by Maimonides (Rambam).
לשמוע קול שופר בראש השנה, שנאמר: "יום תרועה, יהיה לכם" (במדבר כט,א).
To hear the sound of the shofar on Rosh HaShanah, as [Numbers 29:1] states: "It will be a day of [shofar] blasts for you."