Parashas Acharei Mos · Passuk 18:19
Chabad.org — English translation + Rashi
Torah Temima points to Avot de-Rabbi Natan ch. 2.
English: What fence did the Torah make for its words regarding niddah? One might think embracing, kissing or idle talk is allowed — “do not approach” forbids even that.
Torah’s own fence around niddah
The verse itself creates a protective boundary beyond the final act of uncovering.