Valmiki Ramayana Ayodhya Kanda Sarga 118 Shloka 40

गौरवात् because of weight, मनुष्यैः by a human, यत्नेनापि even with great effort, असञ्चाल्यम् cannot be moved, तत् that bow, नराधिपाः lords of men, स्वप्नेष्वपि even in their dreams, नमयितुम् to bend, न शक्ताः were not capable.

Because of its weight, no human could move that bow despite great effort nor were the kings capable of bending it even in their dreams.