Mahabharata 5.80.18

5.80.18

yathāvadhye bhaveddoṣo vadhyamāne janārdana |
sa vadhyasyāvadhe dṛṣṭa iti dharmavido viduḥ || 18 ||

The Pandavas with the Srinjayas, O thou of mighty arms, are quite able to withstand the fierce Dhritarashtra host inflamed with rage. When they are no longer amenable to this arts of conciliation, it is not proper, O slayer of Madhu, that thou shouldst show them mercy. Those enemies, O Krishna, with whom peace cannot be established by either conciliation or presents, should be treated with severity by one desirous of saving his life. Therefore, O mighty-armed Achyuta, heavy should be the punishment that deserves to be speedily inflicted upon them by thyself aided by the Pandavas and the Srinjayas. Indeed, even this would become the son of Pritha, and add to thy glory, and if accomplished, will, O Krishna, be a source of great happiness to the whole Kshatriya race. He that is covetous, whether belonging to the Kshatriya or any other order, save of course a Brahmana, even if most sinful, ought surely to be slain by a Kshatriya, who is true to the duties of his own order. The exception in the case of a Brahmana, O sire, is due to a Brahmana's being the preceptor of all the other orders, as also the first sharer of everything. Persons conversant with the scriptures declare, O Janardana, that sin is incurred in slaying one that deserveth not to be slain. So there is equal sin in not slaying one that deserveth to be slain. Act thou, therefore, O Krishna, in such a way with the forces of the Pandavas and the Srinjayas, that sin may not touch thee.