KAṬHA UPANISHAD · 1.3.6

यस्तु विज्ञानवान्भवति युक्तेन मनसा सदा ।
तस्येन्द्रियाणि वश्यानि सदश्वा इव सारथेः ॥ ६॥

yastu vijñānavānbhavati yuktena manasā sadā ।
tasyendriyāṇi vaśyāni sadaśvā iva sāratheḥ ॥ 6॥

But he that has knowledge with his mind ever applied, his senses are to him as noble steeds and they obey the driver.