Positive Mitzvah 223
The Suspected Woman
Numbers 5:12 "If any man's wife is suspected of committing adultery"
If a woman is suspected of behavior unfit for a married woman, she is called a Sotah. The Torah provides a way of dealing with the matter.
This Positive Mitzvah details the procedure that must be followed.
Negative Mitzvah 104
We are forbidden to pour olive oil on the meal-offering of a "Sotah"
Numbers 5:15 "He shall pour no oil upon it"
This Negative Mitzvah applies to the meal-offering of a Sotah (see Positive Mitzvah 223).
A "Sotah" is a woman who is suspected of not being faithful to her husband. The Torah requires that she and her husband go to the priest and bring a sacrifice.
Since this is a sacrifice that is connected with a possible sin, it consists of plain barley flour with nothing else added. No oil may be poured over this offering.