Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 143
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 143, with English translation by Maimonides (Rambam).
שלא לאכול מעשר שני של יצהר חוץ לירושלים, שנאמר "ויצהרך" (דברים יב,יז).
Not to consume oil [separated as] the second tithe outside of Jerusalem, as [Deuteronomy, ibid.] continues: "...and your oil...."