Srimad Bhagvata Mahapurana: Book 10: Chapter 66: Verses 15-29
All this outfit was so artificial that he looked like an actor on the stage. Finding Paundraka closely imitating Him in dress, Lord Sri Krsna heartily laughed. (Now) the enemies assailed Sri Krsna with their pikes, maces, iron clubs, lances, spears, darts, bludgeons, swords, Pattisas and arrows. Like the fire raging at the time of universal destruction, which destroys all creatures severally, Sri Krsna utterly crushed with His mace, sword, discus and shafts that (joint) army of Paundraka and the king of Kasi, consisting (as it did) of elephants, chariots, horses and footmen. The (whole) field was strewn with chariots and (dead bodies of) horses, elephants, men, donkeys and camels- cut to pieces by the discus of Sri Krsna-and looked as fearful as the place where Sankara carries on His deadly dance of destruction (at the end of a Kalpa). Its sight afforded delight to the brave.
Now Sri Krsna addressed Paundraka, (as follows) : " Hullo Paundraka, you asked Me through the mouth of your messenger to give up the weapons (I carry on My person). I shall accordingly discharge them on you. I shall compel you to give up My name, which has been falsely assumed by you, 0 ignorant one. You asked Me to take refuge in you. I would do so today, if I avoided a clash with you." Reproaching him thus, Sri Krsna shattered the chariot of Paundraka with His sharp arrows and lopped off his head with His discus, (even) as Indra would knock down wings of a mountain with his thunderbolt. Sri Krsna likewise severed the head of the king of Kasi from his body with His arrows and caused it to (fly and) fall into the city of Kasi even as the wind would carry away a lotus-bud.
Thus putting an end to (both) Paundraka and his ally (the king of Kasi), who, had been nursing enmity towards Him, Lord Sri Krsna returned to Dwaraka, the Siddhas singing His stories, sweet as nectar. Pariksit, Paundraka ever used to think intensely of the Lord. All the ties of his Karma were cut asunder by this; and as he (constantly) remembered the Lord's Form, when imitating Him, he attained the same Form as His (after death). Seeing a human head with ear-rings lying at the entrance of the palace (in Kasi), the people wondered whose head it was, and how it came. Recognizing (at last) that it was the head of their king (the ruler of Kai), the queens, sons and relations of the king and the citizens wailed loudly saying, "0 lord, 0 master, 0 king, alas, we are (all) undone." The king's son, Sudaksina, performed the funeral rites to his father and resolved in his mind that he would repay the debt to his father by killing his slayer. With the help of his priest Sudaksina began to worship Sankara with the utmost concentration. Pleased with his worship at Kasi, Lord Sankara offered him a boon. Sudaksina replied, " Lord, (if You are pleased with me) tell me by what means I can kill the slayer of my father. That is the only boon I seek from You."