Valmiki Ramayana Yuddha Kanda Sarga 60 Shloka 57
Original Shlokaतस्यजाजृम्भमाणस्यवक्त्रंपातालसन्निभम् । ददृशेमेरुशृङ्गाग्रेदिवाकरइवोदितः ।।6.60.57।।
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जाजृम्भमाणस्य as he yawned, तस्य his, पातालसन्निभम् resembling the underworld, वक्त्रम् mouth, मेरुशृङ्गाग्रे top of the Meru mountain, उदितः risen over, दिवाकरःइव like the sun, ददृशे appeared.
As he yawned his mouth resembling the underworld, it was like the Sun rose over the top of Mount Meru.