Mbh 7.13.2

“‘Arjuna said, “As the slaughter of my preceptor can never be accomplished by me, so, king, I can never consent to give thee up. O son of Pandu, I would rather yield up my life in battle than fight against my preceptor. This son of Dhritarashtra desireth sovereignty, having seized thee as a captive in battle. In this world he will never obtain the fruition of that desire of his. The firmament itself with its stars may fall down, the Earth herself may split into fragments, yet Drona will, surely, never succeed in seizing thee as long as I am alive. If the wielder of the thunderbolt himself, or Vishnu at the head of the gods, assist him in battle, still he shall not succeed in seizing thee on the field. As long as I am alive, O great king, it behoveth thee not to entertain any fear of Drona, although he is the foremost of all wielders of weapons. I further say unto thee, O monarch, that my promise never remains unfulfilled. I do not recollect having ever spoken any untruth. I do not recollect having ever been vanquished. I do not recollect having ever, after making a vow, left the least part of it unfulfilled.”’