Valmiki Ramayana Sundara Kanda Sarga 62 Shloka 33
Original Shlokaइष्टं मधुवनं ह्येतत्पार्थिवस्य महात्मनः। पितृपैतामहं दिव्यं देवैरपि दुरासदम्।।5.62.33।।
1 source checked for this shloka
पितृपैतामहम् from grandfather and father, दिव्यम् wonderful, देवैरपि even for devatas, दुरासदम् forbidden, एतत् this, मधुवनम् Madhuvanam, महात्मनः great self, पार्थिवस्य to the king, इष्टं हि very dear.
'Madhuvan has come down to us from our forefather's time. Dear to the king, its entry is prohibited even to the gods.