Valmiki Ramayana Sundara Kanda Sarga 50 Shloka 16
Original Shlokaअस्त्रपाशैर्न शक्योऽहं बद्धुं देवासुरैरपि।।5.50.16।। पितामहादेष वरो मामाप्येषोऽभ्युपागतः।
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अहम् I, देवसुरैरपि even by suras and asuras, अस्त्रपाशैः by bondage of astras, बद्धुम् to bind, न शक्यः not possible, एषः वरः such a boon, ममापि to me also, पितामहादेव only from grand father Brahma, अभ्युपागतः it has been granted me.
"It is not possible to bind me with any bondage of astras even by devas or danavas. Such a boon has been granted to me by Grandfather Brahma.