Mahabharata 7.16.27

प्रज्वाल्य कृष्णवर्त्मानमुपागम्य रणे व्रतम्तस्मिन्नग्नौ तदा चक्रुः प्रतिज्ञां दृढनिश्चयाः

prajvālya kṛṣṇavartmānamupāgamya raṇe vratamtasminnagnau tadā cakruḥ pratijñāṃ dṛḍhaniścayāḥ

Our plain-language meaning of this verse is waiting for scholar review.