Srimad-Bhagavatam: Canto 1 - Chapter 1 - Verse 16

Sanskrit:

तदा शुचस्ते प्रमृजामि भद्रेयद्ब्रह्मबन्धो: शिर आततायिन: ।गाण्डीवमुक्तैर्विशिखैरुपाहरेत्वाक्रम्य यत्‍स्‍नास्यसि दग्धपुत्रा ॥ १६ ॥

ITRANS:

tadā śucas te pramṛjāmi bhadreyad brahma-bandhoḥ śira ātatāyinaḥgāṇḍīva-muktair viśikhair upāharetvākramya yat snāsyasi dagdha-putrā

Translation:

O gentle lady, when I present you with the head of that brāhmaṇa, after beheading him with arrows from my Gāṇḍīva bow, I shall then wipe the tears from your eyes and pacify you. Then, after burning your sons’ bodies, you can take your bath standing on his head.

Purport:

An enemy who sets fire to the house, administers poison, attacks all of a sudden with deadly weapons, plunders wealth or usurps agricultural fields, or entices one’s wife is called an aggressor. Such an aggressor, though he be a brāhmaṇa or a so-called son of a brāhmaṇa, has to be punished in all circumstances. When Arjuna promised to behead the aggressor named Aśvatthāmā, he knew well that Aśvatthāmā was the son of a brāhmaṇa, but because the so-called brāhmaṇa acted like a butcher, he was taken as such, and there was no question of sin in killing such a brāhmaṇa’s son who proved to be a villain.