The Great Epic of the Bhārata dynasty 7.168.39

7.168.39

nānṛtaḥ pāṇḍavo jyeṣṭho nāhaṃ vādhārmiko'rjuna |
śiṣyadhruṅnihataḥ pāpo yudhyasva vijayastava || 39 ||

Fight now. Victory will be thine.'"

Why then dost thou not applaud an act that is worthy of applause? He had slain in battle only my kinsmen and not those of any one else. I say that having only cut off his head, the fever of my heart hath not abated. The very core of my heart is being pierced for my not having thrown that head within the dominion of the Nishadas, like that of Jayadratha! It hath been heard, O Arjuna, that one incurreth sin by not slaying his foes. Even this is the duty of a Kshatriya, viz., to slay or be slain. Drona was my foe. He hath been righteously slain by me in battle, O son of Pandu, even as thou hast slain the brave Bhagadatta, thy friend. Having slain thy grandsire in battle, thou regardest that act to be righteous. Why then shouldst thou regard it unrighteous in me for my having slain my wretched foe? In consequence of our relationship, O Partha, I cannot raise my head in thy presence and am like a prostrate elephant with a ladder against his body (for helping puny creatures to get on his back). It, therefore, behoveth thee not to reproach me. I forgive all the faults of thy speech, O Arjuna, for the sake of Draupadi and Draupadi's children and not for any other reason. It is well known that my hostility with the preceptor has descended from sire to son. All persons in this world know it. Ye sons of Pandu, are ye not acquainted with it? The eldest son of Pandu hath not been untruthful in speech. I myself, O Arjuna, am not sinful. The wretched Drona was a hater of his disciples.