Bhagavad Gita Chapter 6, Verse 18

यदा विनियतं चित्तमात्मन्येवावतिष्ठते | निःस्पृहः सर्वकामेभ्यो युक्त इत्युच्यते तदा ||

yadā viniyataṁ cittam ātmany evāvatiṣṭhate niḥspṛhaḥ sarva-kāmebhyo yukta ity ucyate tadā

When the perfectly controlled mind rests in the Self alone, free from longing for all desires, then one is said to be in union.

Krishna describes the state of union (yoga). 'Yadā viniyataṁ cittam'—when the perfectly controlled (viniyatam) mind (cittam)—'ātmany evāvatiṣṭhate'—rests (avatiṣṭhate) in the Self (ātmani) alone (eva). This means: when your mind is completely disciplined, when it's perfectly controlled, it naturally rests in your true nature—the Self. It doesn't wander, it doesn't scatter—it settles in who you really are. 'Niḥspṛhaḥ sarva-kāmebhyaḥ'—free from longing (niḥspṛhaḥ) for all desires (sarva-kāmebhyaḥ). This means: not just some desires, but all desires—completely free, no longing, no craving. 'Yukta ity ucyate tadā'—then (tadā) one is said (ucyate) to be in union (yuktaḥ). This means: when your mind rests in the Self and you're free from all desires, you've achieved yoga—union with your true nature. This is the state of self-realization—mind established in Self, completely desireless, truly united.