Valmiki Ramayana Sundara Kanda Sarga 2 Shloka 33
Original Shlokaअनेन रूपेण मया न शक्या रक्षसां पुरी। प्रवेष्टुं राक्षसैर्गुप्ता क्रूरैर्बलसमन्वितैः।।5.2.33।।
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क्रूरैः by the fierce, बलसमन्वितैः by the powerful ones, राक्षसैः by demons, गुप्ता guarded, रक्षसाम् of demons, पुरी city, मया by me, अनेन by this present, रूपेण form, प्रवेष्टुम् to enter, न शक्या not possible.
'I shall not be able in my present form to enter the city guarded by fierce and powerful demons.