And Moses said: This is the thing which the L-rd commanded that you should do, so that the glory of the L-rd may appear to you. (Leviticus 9:6) Do not look into other people’s faces, even when you speak with them. For if their thoughts are not constantly attached to G‑d, you will blemish your soul. However, you should definitely look into the faces of righteous people whose thoughts are attached to G‑d, for this will bring holiness to your soul. Tzava’as HaRivash, p. 6b¹sharos, p. 12a.

footnotes: ¹ See, also, Hanhagos Ye