Valmiki Ramayana Yuddha Kanda Sarga 28 Shloka 16
Original Shlokaसत्यमागमयोगेनममैषविदितोहरिः । नास्यशक्यंबलंरूपंप्रभावोवाऽपिभाषितम् ।।6.28.16।।
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एषः this, हरिः monkey, मम to me, सत्यम् truth, आगमयोगेन by one who is in contact with me, विदितः known, अस्य his, बलम् strength, रूपम् appearance, प्रभावोना even his glory, नभाषितम् अपि cannot be described, नशक्यम् not possible.
"I came to know about him through one of my contacts. His strength, his appearance and glory are indescribable."