अस्तमित आदित्ये याज्ञवल्क्य चन्द्रमस्यस्तमिते किंज्योतिरेवायं पुरुष इति ।अग्निरेवास्य ज्योतिर्भवतीति ।अग्निनैव ज्योतिषास्ते पल्ययते कर्म कुरुते विपल्येतीति ।एवमेवैतद्याज्ञवल्क्य ॥४,३.४ ॥
In plain words
"When the sun has set, Yājñavalkya, and the moon has set, what light does this person have?" "Fire becomes his light. With fire as his light he sits, moves about, does his work and returns." "So it is, Yājñavalkya."
The commentators
Bṛhadāraṇyakopaniṣadbhāṣyam· avatāraṇikā
अस्तमित आदित्ये, चन्द्रमस्यस्तमिते अग्निर्ज्योतिः ॥
In plain words
Once the sun goes down, and the moon goes down after it -- fire is what is left to light the way.
Close to the Sanskrit
When the sun has set, [and] when the moon has set, fire is the light.