Katha Upanishad - Verse 2.3.1
Text: ऊर्ध्वमूलोऽवाक्शाख एषोऽश्वत्थः सनातनः । तदेव शुक्रं तद्ब्रह्म तदेवामृतमुच्यते । तस्मिंल्लोकाः श्रिताः सर्वे तदु नात्येति कश्चन । एतद्वैतत् ॥ १ ॥ ūrdhvamūlo’vākśākha eṣo’śvatthaḥ sanātanaḥ | tadeva śukraṃ tadbrahma tadevāmṛtamucyate | tasmiṃllokāḥ śritāḥ sarve tadu nātyeti kaścana | etadvaitat || 1 || 1. Root up and branches down is this ancient asvattha tree, that (its source) is pure. That is Brahman and that alone is called immortal. On that, do all worlds depend and none passes beyond that....