Ramayana
अमोघशापैः शप्तस्तु दत्तो ऽस्य मुनिभिः पुरा । न वेत्ता हि बलं येन बली सन्निरिमर्दनः ॥ 7-35-16 ॥
He was cursed of old by the sages with curses that never fail, so that, though mighty and a crusher of foes, he does not know his own strength.
english translation