Valmiki Ramayana Sundara Kanda Sarga 46 Shloka 12
Original Shlokaमहत्सत्त्वमिदं ज्ञेयं कपिरूपं व्यवस्थितम्।।5.46.12।। प्रयत्नं महदास्थाय क्रियतामस्य निग्रहः।
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इदम् this, कपिरूपम् a monkey form, व्यवस्थितम् concluded, महत् great, सत्त्वम् being, ज्ञेयम् It should be understood, महत् extraordinary, प्रयत्नम् effort, आस्थाय by putting up, अस्य his, निग्रहः capture, क्रियताम् do.
"It should be understood that he has taken the form of a monkey. You have to put in extraordinary effort to capture him by acting in a suitable manner.