Bhagavad Gita 18.45
Perfection is attained when one diligently attends to their duty. Listen, and I will tell you how it is attained by one who always minds their own duty.
स्वे स्वे कर्मण्यभिरतः संसिद्धिं लभते नरः।स्वकर्मनिरतः सिद्धिं यथा विन्दति तच्छृणु॥sve sve karmaṇyabhirataḥ saṃsiddhiṃ labhate naraḥ|svakarmanirataḥ siddhiṃ yathā vindati tacchṛṇu||
English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).