Valmiki Ramayana Aranya Kanda Sarga 4 Shloka 30
Original Shlokaस्वयं विराधेन हि मृत्युरात्मनः प्रसह्य रामेण यथार्थमीप्सितः। निवेदितः काननचारिणा स्वयं न मे वधः शस्त्रकृतो भवेदिति।।3.4.30।।
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विराधेन by Viradha, स्वयम् himself, आत्मनः for him, मृत्युः death, यथार्थम् truly, प्रसह्य forcibly, रामेण by Rama, ईप्सितः wished to, काननचारिणा one by the forestranger, मे for me, शस्त्र कृतः by the weapons, वधः kill, न भवेत् not possible for you, इति thus, स्वयम् he himself, निवेदितः was revealed.
Rama deliberately wanted to kill Viradha with weapons. Viradha the forestranger himself revealed that it was not possible to kill him with weapons and asked Rama to bury him in a pit.