Parashas Acharei Mos · Passuk 18:06
Chabad.org — English translation + Rashi
Torah Temima points to Avot de-Rabbi Natan ch. 2.
English: From here the Sages said: a man should not seclude himself with women at an inn even with his sister or daughter, nor walk or converse with a woman in the marketplace even with his wife, because of public suspicion.
Fences around yichud and public appearance
“Do not approach” generates practical stringencies of seclusion and public conduct beyond the core prohibition.