KAṬHA UPANISHAD · 1.3.14

उत्तिष्ठत जाग्रत
प्राप्य वरान्निबोधत ।
क्षुरस्य धारा निशिता दुरत्यया
दुर्गं पथस्तत्कवयो वदन्ति ॥ १४॥

uttiṣṭhata jāgrata
prāpya varānnibodhata ।
kṣurasya dhārā niśitā duratyayā
durgaṃ pathastatkavayo vadanti ॥ 14॥

Arise, awake, find out the great ones and learn of them; for sharp as a razor’s edge, hard to traverse, difficult of going is that path, say the sages.