Mishneh Torah — Negative Mitzvot מצוות לא תעשה, Chapter 104
The full Hebrew text of Mishneh Torah, Negative Mitzvot, Chapter 104, with English translation by Maimonides (Rambam).
שלא ייתן שמן במנחת סוטה, שנאמר "לא ייצוק עליו שמן" (במדבר ה,טו).
Not to place oil on the meal offering brought by a sotah, as [Numbers 5:15] states: "Do not pour oil upon it."