Mishnah Yoma 8:1 — Sefaria version 'Mishnah Yomit by Dr. Joshua Kulp' (CC-BY; source: learn.conservativeyeshiva.org) (CC BY)
[On] Yom HaKippurim it is forbidden to eat, to drink, to wash, to anoint oneself, to put on sandals, or to have intercourse. A king or bride may wash their face, and a woman after childbirth may put on sandals, the words of Rabbi Eliezer. But the sages forbid it.
Reproduced in full. Translation: Sefaria version 'Mishnah Yomit by Dr. Joshua Kulp' (CC-BY; source: learn.conservativeyeshiva.org) (CC BY).
Why Pitre cites it
The Day of Atonement's self-affliction includes abstaining from marital relations — the text (via Milgrom) that lets 'afflict herself' in Numbers 30 mean sexual abstinence.
Notes
Kulp renders the sixth prohibition 'or to have intercourse'; the key phrase as given ('marital relations' / 'the marriage bed') is not verbatim in any Sefaria version. Alternatives on the same page: William Davidson/Steinsaltz (CC-BY-NC) 'and in conjugal relations'; Sefaria Community Translation (CC0); 'Eighteen Treatises from the Mishna' (De Sola & Raphall 1843, public domain). Kulp chosen as the most permissive modern version.