Leviticus 18:6 "No person shall approach a close relative and act immodestly"

A person must not act immodestly in any way.

In the previous Negative Mitzvot, the Torah listed certain cases where one person may not have a relationship with another.

In this Negative Mitzvah, the Torah further warns us that a person must should not act even slightly immodestly with any of the people with whom marriage is forbidden, even if one does not intend to take that woman as a wife or that man as a husband.