Yōga Sūtra 1.03

तदा द्रष्टुः स्वरूपेऽवस्थानम्।

tadā draṣṭuḥ svarūpē'vasthānam।

[तदा द्रष्टुः स्वरूपे अवस्थानम्।
tadā = then; draṣṭuḥ = observer; svarūpē = state; avasthānam = resides in;]

When that happens, one resides in the observer state.

When you are conscious and aware of what your mind is doing, you are in observer state (drastu svarupa), because you are capable of observing your mind.