Brahmaśirastra-pratisaṃhāra — Retraction and redirection of the supreme weapon
Sauptika Parva, Adhyāya 15
जिस देशमें एक ब्रह्मास्त्रको दूसरे उत्कृष्ट अस्त्रसे दबा दिया जाता है, उस राष्ट्रमें बारह वर्षोतक वर्षा नहीं होती है ।।
yasmin deśe ekaṁ brahmāstraṁ dvitīyena utkṛṣṭena astreṇa dabaṁ (nigṛhītaṁ) kriyate, tasmin rāṣṭre dvādaśa-varṣāṇi yāvat varṣā na bhavati. etad-arthaṁ mahābāhuḥ śaktimān api pāṇḍavaḥ prajā-hita-cikīrṣayā etad astraṁ tu na vihanti. ata eva prajā-vargasya hitam icchan mahābāhur arjunaḥ śaktimān san api tava etad astraṁ nāśayituṁ na pravartate.
Vyāsa said: In whatever land one Brahmāstra is forcibly checked by another superior weapon, that kingdom suffers a drought for twelve years. For this reason the mighty-armed Pāṇḍava—though fully capable—does not destroy this weapon, seeking the welfare of the people.
व्यास उवाच
Even when one has the power to retaliate, dharma may require restraint: the use of supreme weapons must be governed by concern for the innocent, since their clash brings long-term harm to the land and its people.
Vyasa explains why Arjuna does not simply annihilate the opponent’s Brahmāstra with a counter-weapon: suppressing one Brahmāstra by another would devastate the realm through a twelve-year drought, so Arjuna holds back for the sake of the subjects.