When Ashwatthama learned his father was dead, he unleashed the Narayana-astra, which spewed deadly fire across the sky.
"It will kill us all!" shouted Yudhishthira.
"Don't be afraid," said Krishna. "Bow down to this weapon, and it will spare you. Do not fight; be at peace."
Bhima, however, did not listen; instead, he ran towards Ashwatthama, brandishing his mace. The astra's fire then focused on Bhima, but Krishna and Arjuna intervened, throwing Bhima to the ground and wrenching the mace from his hand.
"This astra won't attack an unarmed man," Krishna explained, and as he spoke, the astra's fire subsided.
Inspired by: Jaya: An Illustrated Retelling of the Mahabharata by Devdutt Pattanaik.
Notes: This story is on p. 267.