Actually King Jarāsandha was very liberal in giving charity to brāhmaṇas, and thus he informed Lord Kṛṣṇa, Bhīma and Arjuna: “My dear brāhmaṇas, you may ask from me whatever you like. If you so desire, you may take my head also. I am prepared to give it.”
After this, Lord Kṛṣṇa addressed Jarāsandha as follows: “My dear King, please note that we are not actually brāhmaṇas, nor have we come to ask for food or grain. We are all kṣatriyas, and we have come to beg a duel with you. We hope that you will agree to this proposal. You may note that here is the second son of King Pāṇḍu, Bhīmasena, and the third son of Pāṇḍu, Arjuna. As for Myself, you may know that I am your old enemy Kṛṣṇa, the cousin of the Pāṇḍavas.”
When Lord Kṛṣṇa disclosed their disguise, King Jarāsandha laughed very loudly, and then in great anger and in a grave voice he exclaimed, “You fools! If you want to fight with me, I immediately grant your request. But, Kṛṣṇa, I know that You are a coward. I refuse to fight with You because You become very confused when You face me in fighting. Out of fear of me You left Your own city, Mathurā, and now You have taken shelter within the sea; therefore I must refuse to fight with You. As far as Arjuna is concerned, I know that he is younger than me and is not an equal fighter. I refuse to fight with him because he is not in any way an equal competitor. But as far as Bhīmasena is concerned, I think he is a suitable competitor to fight with me.” After speaking in this way, King Jarāsandha immediately handed a very heavy club to Bhīmasena, he himself took another, and all of them went outside the city walls to fight.
Bhīmasena and King Jarāsandha engaged themselves in fighting, and with their respective clubs, which were as strong as thunderbolts, they began to strike each other very severely, both of them being eager to fight. They were both expert fighters with clubs, and their techniques of striking each other were so beautiful that they appeared to be two dramatic artists dancing on a stage. When the clubs of Jarāsandha and Bhīmasena loudly collided, the impact sounded like that of the big tusks of two fighting elephants or like a thunderbolt in a flashing electrical storm. When two elephants fight together in a sugarcane field, each of them snatches a stick of sugarcane, holds it tightly in its trunk and strikes the other. At that time the sugarcane becomes smashed by such heavy striking. Similarly, when Bhīmasena and Jarāsandha were heavily striking each other with their clubs on different parts of their bodies—namely the shoulders, arms, collarbone, chest, thighs, waist and legs—their clubs became torn to pieces. In this way, all of the clubs used by Jarāsandha and Bhīmasena became ruined, and so the two enemies prepared to fight with their strong-fisted hands. Jarāsandha and Bhīmasena were very angry, and they began to smash each other with their fists. The striking of their fists sounded like the striking of iron bars or like the sound of thunderbolts, and the two warriors appeared to be like two elephants fighting. Neither was able to defeat the other, however, for both were expert in fighting, they were of equal strength, and their fighting techniques were also equal. Neither Jarāsandha nor Bhīmasena became fatigued or defeated in the fighting, although they struck each other continuously. At the end of each day’s fighting, they lived at night as friends in Jarāsandha’s palace, and the next day they fought again. In this way they passed twenty-seven days in fighting.
On the twenty-eighth day, Bhīmasena told Kṛṣṇa, “My dear Kṛṣṇa, I must frankly admit that I cannot conquer Jarāsandha.” Lord Kṛṣṇa, however, knew the mystery of Jarāsandha’s birth. Jarāsandha had been born in two different parts from two different mothers. When his father saw that the baby was useless, he threw the two parts into the forest. There they were later found by a witch named Jarā, who was skilled in the black arts. She managed to join the two parts of the baby from top to bottom. Knowing this, Lord Kṛṣṇa therefore also knew how to kill him. He hinted to Bhīmasena that since Jarāsandha was brought to life by the joining of the two parts of his body, he could be killed by the separation of these two parts. Thus Lord Kṛṣṇa transferred His power into the body of Bhīmasena and informed him of the device by which Jarāsandha could be killed. Lord Kṛṣṇa picked up a twig from a tree, took it in His hand, and bifurcated it. In this way He hinted to Bhīmasena how Jarāsandha could be killed. Lord Kṛṣṇa, the Supreme Personality of Godhead, is omnipotent, and if He wants to kill someone, no one can save that person. Similarly, if He wants to save someone, no one can kill him.