Mbh 7.178.1c

Indeed, the battle that took place between Bhima’s son and Alayudha, was, O king, dreadful in the extreme, like that in days of old, O monarch, between Vali and Sugriva, those two princes among the monkeys. They struck each other with shafts and diverse other kinds of fierce weapons, as also with sharp scimitars. Then the mighty Rakshasas, rushing against each other, seized each other by the hair. And, O king, those two gigantic warriors, with many wounds on their bodies and blood and sweat trickling down, looked like two mighty masses of clouds pouring rain. Then rushing with speed and whirling the Rakshasas on high and dashing him down, Hidimva’s son cut off his large head. Then taking that head decked with a pair of ear-rings, the mighty Ghatotkacha uttered a loud roar. Beholding the gigantic brother of Vaka, that chastiser of foes, thus slain, the Panchalas and the Pandavas began to utter leonine shouts. Then, upon the fall of the Rakshasa, the Pandavas beat and blew thousands of drums and ten thousands of conchs. That night then clearly indicated the victory of the Pandavas. Illumined with torches all around, and resounding with the noise of musical instruments, the night looked exceedingly resplendent. Then the mighty son of Bhimasena threw down the head of the slain Alayudha before Duryodhana. Duryodhana, beholding the heroic Alayudha slain, became, O Bharata, filled with anxiety, for all his troops. Alayudha, having come to Duryodhana of his own accord. remembering his former quarrel, had said unto him that he would slay Bhima in battle. The Kuru king had regarded Bhima’s slaughter to be certain, and had believed that his brothers would all be long-lived. Beholding that Alayudha slain by Bhimasena’s son, the king regarded Bhima’s vow (about the slaughter of himself and his brothers) already fulfilled.’”