In the Sanditthika Sutta,
"The fact that when a delusive quality is present within you, you discern that a delusive quality is present within you; and when a delusive quality is not present within you, you discern that a delusive quality is not present within you"
A similar description is also given in the Satipatthana Sutta. The second part, "to know when something is not present inside of me", is to be understood how? Do I literally acknowledge at any point in my daily life that I have currently no defilements in me? And if the answer is yes, what do I do with that acknowledging?