Bhagavad Gita · 18.6

एतान्यपि तु कर्माणि सङ्गं त्यक्त्वा फलानि च।कर्तव्यानीति मे पार्थ निश्चितं मतमुत्तमम्॥

etāny api tu karmāṇi saṅgaṁ tyaktvā phalāni cha kartavyānīti me pārtha niśhchitaṁ matam uttamam

But even these actions should be performed without attachment and without expectation of reward. This is My definite and supreme conclusion, O Partha.

— Bhagavad Gita 18.6

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