Mahabharata 12.1.26

12.1.26

gatā kila pṛthā tasya sakāśamiti naḥ śrutam |
asmākaṃ śamakāmā vai tvaṃ ca putro mametyatha || 26 ||

We have heard that on one occasion Pritha went to him for seeking our good and addressed him, saying, 'Thou art my son!' That illustrious hero, however, refused to obey Pritha's wishes. Subsequently, we are informed, he said unto his mother these words, 'I am unable to desert Duryodhana in battle! If I do so, it would be a dishonourable, cruel, and ungrateful act. If, yielding to thy wishes, I make peace with Yudhishthira, people will say that I am afraid of the white-steeded Arjuna. Having vanquished Arjuna with Kesava, therefore, in battle, I will subsequently make peace with Dharma's son.' Even these were his words as we have heard. Thus answered, Pritha once more addressed her son of broad chest and said, 'Fight Phalguna then, but spare my four other sons.' The intelligent Karna, with joined hands, then replied unto his trembling mother, saying, 'If I get thy four other sons even under my power, I will not slay them. Without doubt, O goddess, thou shalt continue to have five sons. If Karna be slain with Arjuna, thou shalt have five! If, on the other hand, Arjuna be slain, thou shalt have five, numbering me.' Desirous of the good of her children, his mother once more said unto him, 'Go, O Karna, do good unto those brothers of thine whose good thou always seekest.' Having said these words, Pritha took his leave and came back to her abode. That hero has been slain by Arjuna,--the uterine brother by the brother! Neither Pritha, nor he, had ever disclosed the secret, O lord!