yadyapy astram brahma-siras
tv amogham capratikriyam
vaisnavam teja asadya
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
O Saunaka, glory of Bhrgu’s family, although the supreme brahmastra weapon released by Asvatthama was irresistible and without check or counteraction, it was neutralized and foiled when confronted by the strength of Visnu [Lord Krsna].
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
In the Bhagavad-gita it is said that the brahmajyoti, or the glowing transcendental effulgence, is resting on Lord Sri Krsna. In other words, the glowing effulgence known as brahma-tejas is nothing but the rays of the Lord, just as the sun rays are rays of the sun disc. So this Brahma weapon also, although materially irresistible, could not surpass the supreme strength of the Lord. The weapon called brahmastra, released by Asvatthama, was neutralized and foiled by Lord Sri Krsna by His own energy; that is to say, He did not wait for any other’s help because He is absolute.