Bhagavad Gita 18.49

असक्तबुद्धि: सर्वत्र जितात्मा अतीतस्पृह: |
नैष्कर्म्यसिद्धिं परमंन्यासेनाधिग्च्छति

Translation

Those whose intellect is unattached everywhere, who have mastered the mind, and are free from desires by the practice of renunciation, attain the highest perfection of freedom from action.