Bhagavad Gita · 6.18

यदा विनियतं चित्तमात्मन्येवावतिष्ठते।निःस्पृहः सर्वकामेभ्यो युक्त इत्युच्यते तदा॥

yadā viniyataṁ chittam ātmany evāvatiṣhṭhate niḥspṛhaḥ sarva-kāmebhyo yukta ity uchyate tadā

When the perfectly disciplined mind rests in the Self alone, free from longing for all desires — then one is said to be united in yoga.

— Bhagavad Gita 6.18

Source: Sacred-Texts.com (Sanskrit) + Bhagavad-Gita.io (translations)