Mbh 6.108.1c

The twin sons of Madri also are each as valiant as the Chief of the celestials himself. From the good understanding that exists between us, do thou set me also to this task. Even I, O son of Pandu, will fight with Bhishma. Directed by thee, O great king, what is there that I may not do in great battle. Challenging that bull among men, viz., Bhishma, I will slay him in battle, in the very sight of the Dhartarashtras, if Phalguni doth not wish to slay him. If, O son of Pandu, thou seest victory to be certain on the slaughter of the heroic Bhishma, even I, on a single car, will slay that aged grandsire of the Kurus. Behold, O king, my prowess, equal to that of the great Indra in battle. I will overthrow from his car that warrior who always shooteth mighty weapons. He that is an enemy of the sons of Pandu, without doubt, is my enemy also. They, that are yours, are mine, and so they, that are mine, are yours. Thy brother (Arjuna) is my friend, relative, and disciple. I will, O king, cut off my own flesh and give it away for the sake of Arjuna. And this tiger among men also can lay down his life for my sake. O sire, even this is our understanding, viz., that we will protect each other. Therefore, command me, O king, in what way I am to fight. Formerly, at Upaplavya, Partha had, in the presence of many persons, vowed, saying, “I will slay the son of Ganga.” These words of the intelligent Partha should be observed (in practice). Indeed, if Partha requests me without doubt I will fulfill that vow. Or, let it be the task of Phalguni himself in battle. It is not heavy for him. He will slay Bhishma, that subjugator of hostile cities. If excited in battle, Partha can achieve feats that are incapable of being achieved by others. Arjuna can slay in battle the very gods exerting themselves actively, along with the Daityas and the Danavas. What need be said of Bhishma, therefore, O king?