Valmiki Ramayana Ayodhya Kanda Sarga 28 Shloka 7
Original Shlokaगिरिनिर्झरसम्भूता गिरिकन्दर वासिनाम्। सिंहानां निनदा दुःखा श्श्रोतुं दुःखमतो वनम्।।2.28.7।।
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गिरिनिर्झरसम्भूताः arising from the falling waters from mountains, निनदाः sounds, गिरिकन्दर वासिनाम् living in the mountain caves, सिंहानाम् of lions, श्रोतुम् to hear, दुःखाः fearful, अतः therefore, वनम् forest, दुःखम् source of pain, दुःखमतो painful.
It is frightening to hear the sounds of waterfalls and the roar of lions living in the mountain caves. Therefore forest life is painful (fearful).