In the Shalya Parva of the Mahabharata, Bhima fights Duryodhana with maces. Krishna tells Arjuna: “If he were to fight fairly, Bhimasena will never succeed in winning the victory.” Arjuna strikes his own left thigh where Bhima can see it. Bhima then strikes Duryodhana on the thighs.
Krishna’s brother Balarama is enraged: “No limb below the navel should be struck. This is the precept laid down in treatises!” Krishna answers that Bhima had vowed to break those thighs, and that a sage had once cursed Duryodhana to the same end. “The accomplishment of one’s vow is one’s duty.”