F. Max Müller (ed.), The Sacred Books of the East, Volume I, The Upanishads, Part I, Clarendon Press, Oxford, 1879

p. 109, The Chandogya Upanishad, Prapathaka 7, Khanda 1, Verse 1:

Narada approach ed Sanatkumara and said, ‘Teach me, Sir!’ Sanatkumara said to him: ‘Please to tell me what you know; afterward I shall tell you what is beyond.’1

ॐ॥ अधीहि भगव इति होपससाद सनत्कुमारं नारदस्त होवाच यद्वेत्थ तेन मोपसीद ततस्त ऊर्ध्वं वक्ष्यामीति स होवाच॥2

p. 112, The Chandogya Upanishad, Seventh Prapathaka 7, Third Khanda, Verse 1:

‘Mind (manas) is better than speech. For as the closed fist holds two amalaka or two kola or two aksha fruits, thus does mind hold speech and name. For if a man is minded in his mind to read the sacred hymns, he reads them; if he is minded in his mind to perform any actions, he performs them; if he is minded to wish for sons and cattle, he wishes for them; if he is minded to wish for this world and the other, he wishes for them. For mind is indeed the self , mind is the world, mind is Brahman. Meditate on the mind.3

मनो वाव वाचो भूयो यथा वै द्वे वामलके द्वे वा कोले द्वौ वाक्षौ मुष्टिरनुभवत्येवं वाचं च नाम च मनोऽनुभवति स यदा मनसा मनस्यति मन्त्रानधीयीयेत्यथाधीते कर्माणि कुर्वीयेत्यथ कुरुते पुत्राश्च पशूश्चेच्छेयेत्यथेच्छत इमं च लोकममुं चेच्छेयेत्यथेच्छते मनो ह्यात्मा मनो हि लोको मनो हि ब्रह्म मन उपास्स्वेति॥4