SB 1.7 - Arjuna's vow
Draupadī, hearing the massacre of her sons, cried in distress. Arjuna tried consoling her saying that he would wipe her tears off by presenting the head of Aśvatthāmā, by beheading him with his Gāṇḍīva bow. Then, after burning her son’s bodies, she could take her bath standing on his head. Arjuna addressed Aśvatthāmā as brahma-bandhu or a degraded brāhmaṇa. Usually a brāhmaṇa is not to be killed. But because the so-called brāhmaṇa acted like a butcher there was no sin in killing him.
Arjuna, who was guided by the infallible Lord as friend and driver (acyuta-mitra-sūtaḥ), then dressed in armor got into his chariot and set out to follow Aśvatthāmā. Aśvatthāmā, seeing Arjuna coming at him with great speed, fled in his chariot as Brahmā (or Sūrya) fled in fear from Lord Śiva. Brahmā once became allured by his daughter and followed her, which infuriated Śiva, who attacked Brahmā with his trident. Brahmā fled in fear of his life. As far as Sūrya is concerned, there was a demon called Vidyunmālī, who was gifted with a golden airplane which traveled to the back of the sun, and night disappeared because of the glowing effulgence of the plane. The sun-god became angry and he melted the plane. This enraged Śiva, who attacked the sun-god, who fled away and at last fell down at Kāśī. This place became famous as Lolārka (unsteady sun).