KAṬHA UPANISHAD · 1.1.15

लोकादिमग्निं तमुवाच तस्मै
या इष्टका यावतीर्वा यथा वा ।
स चापि तत्प्रत्यवदद्यथोक्तं
अथास्य मृत्युः पुनरेवाह तुष्टः ॥ १५॥

lokādimagniṃ tamuvāca tasmai
yā iṣṭakā yāvatīrvā yathā vā ।
sa cāpi tatpratyavadadyathoktaṃ
athāsya mṛtyuḥ punarevāha tuṣṭaḥ ॥ 15॥

Of the Flame that is the world’s beginning he told him and what are the bricks to him and how many and the way of their setting; and Nachiketas too repeated it even as it was told; then Death was pleased and said to him yet farther;

Sri Aurobindo · CWSA 18, p. 104