Parashas Naso
וְהִקְרִ֥יב אֹתָ֖הּ הַכֹּהֵ֑ן וְהֶֽעֱמִדָ֖הּ לִפְנֵ֥י יְהֹוָֽה׃
The priest shall bring her forward and have her stand before GOD.
Torah Temimah points to TT / Sotah (verified).
והקריב אותה הכהן — ת״ר, אין משקין שתי סוטות כאחת, שנאמר והקריב אותה הכהן, אותה לבדה.
English: “And the kohen shall bring her near” — our Rabbis taught: Two sotahs are not given to drink at once, as it is said “and the kohen shall bring her near” — her alone.
Custom
Chazal prohibit administering the bitter water to two women simultaneously.