BṚHADĀRAṆYAKA UPANISHAD · 4.3.6

अस्तमित आदित्ये याज्ञवल्क्य चन्द्रमस्य् अस्तमिते शान्ते ऽग्नौ शान्तायां वाचि किंज्योतिर् एवायं पुरुष इति ।
आत्मैवास्य ज्योतिर् भवतीति ।
आत्मनैवायं ज्योतिषास्ते पल्ययते कर्म कुरुते विपल्येतीति ॥

astamita āditye yājñavalkya candramasy astamite śānte ’gnau śāntāyāṃ vāci kiṃjyotir evāyaṃ puruṣa iti ।
ātmaivāsya jyotir bhavatīti ।
ātmanaivāyaṃ jyotiṣāste palyayate karma kurute vipalyetīti ॥

Ganaka Vaideha said: 'When the sun has set, O Yâgñavalkya, and the moon has set, and the fire is gone out, and the sound hushed, what is then the light of man?' Yâgñavalkya said: 'The Self indeed is his light; for, having the Self alone as his light, man sits, moves about, does his work, and returns.'

F. Max Müller · The Upanishads, Sacred Books of the East 15 (1884)