ŚVETĀŚVATARA UPANISHAD · 2.9

प्राणान् प्रपीड्येह स युक्तचेष्टः क्षीने प्राणे नासिकयोच्छ्वसीत ।
दुष्टाश्वयुक्तम् इव वाहम् एनं विद्वान् मनो धारयेताप्रमत्तः ॥

prāṇān prapīḍyeha sa yuktaceṣṭaḥ kṣīne prāṇe nāsikayocchvasīta ।
duṣṭāśvayuktam iva vāham enaṃ vidvān mano dhārayetāpramattaḥ ॥

Compressing his breathings let him, who has subdued all motions, breathe forth through the nose with gentle breath. Let the wise man without fail restrain his mind, that chariot yoked with vicious horses.