Valmiki Ramayana Sundara Kanda Sarga 3 Shloka 36
Original Shlokaमामनिर्जित्य दुर्बुद्धे राक्षसेश्वरपालितां। न शक्यमद्य ते द्रष्टुं पुरीयं वानराधम।।5.3.36।।
1 source checked for this shloka
दुर्बुद्धे O evilminded one, वानराधम foolish monkey, माम् me, अनिर्जित्य without conquering me, राक्षसेश्वरपालितां ruled by the demon king, इयं पुरी this city, अद्य now, द्रष्टुम् to see, ते by you, न शक्यम् not possible.
"O evilminded, foolish monkey It is not possible for you to enter the city ruled by Ravana, the king of demons without conquering me".