Mahabharata Udyoga Parva Chapter 146:2

Mahabharata Udyoga Parva (Bhagwat Yana Parva) Chapter 146:2 This is the time when all those have been supported by Dhritarashtra's sons should exert themselves for their masters. I shall certainly act for them, reckless of even my life. Those sinful men of unsteady heart, who, well-fed and well-furnished (with every necessary) by their masters, undo the benefit received by them when the time cometh for paying back, are thieves of their master's cakes, have neither this nor the other world for them. I will not speak deceitfully unto thee. For the sake of Dhritarashtra's son, I shall fight against thy sons to the best of my strength and might. I must not, however, abandon kindness and the conduct that becometh the good. Thy words, therefore, however beneficial cannot be obeyed by me now. This thy solicitation to me will not yet be fruitless. Except Arjuna, thy other sons, Yudhishthira, Bhima, and the twins, though capable of being withstood by me in tight and capable also of being slain, shall not yet be slain by me. It is with Arjuna alone, among all the combatants of Yudhishthira, that I will fight. Slaying Arjuna in battle, I shall achieve great merit, or slain by Savyasachin, I shall be covered with glory. O famous lady, the number of thy sons will never be less than five. Five it will always be,—either with me, or with Arjuna, and myself slain. Hearing these words of Karna, Kunti who was trembling with grief, embraced her son who was unmoved in consequence of his fortitude, and said, 'Indeed, O Karna, even if what thou sayest seemeth to be possible, the Kauravas will certainly be exterminated. Destiny is all. Thou hast, however, O grinder of foes, granted to four of thy brothers the pledge of safety. Let that pledge be borne in thy remembrance at the time of shooting of weapons in battle.' And having told all this, Pritha also addressed Karna, saying, 'Blessed be thou, and let health be thine.' And Karna replied unto her, saying, 'Be it so!' And they then left the spot, wending in different directions.