Abu Hafs  [rahimahullaah] said to Abu Uthmaan Al-Naysaabooriy  [rahimahullaah]: When you sit with the people, then be an admonisher of your heart and soul, and do not be deceived by their gathering around you, for they [are only] aware of what they can see apparently, whilst Allaah is all aware of your inner self [i.e. your heart, soul]

[Madaarij As-Saalikeen 2/106. Slightly paraphrased]