Vaishnava weapon

Bhagadatta Son of Narakasur with Mantras, turned his hook into the Vaishnava weapon and hurled it at Arjuna's breast.

1. That all-slaying weapon, hurled by Bhagadatta, 
2. Kesava, covering Arjuna, received on his breast. 
3. Thereupon, that weapon became a triumphal garland on Kesava's breast. 

Arjuna then cheerlessly addressed Kesava, saying, 

'O sinless one, without battling thyself, thou art to only guide my steed! Thou hadst said so, O lotus-eyed one! Why then dost thou not adhere to thy promise? 

1. If I sink in distress, or 
2. become unable to baffle, or 
3. resist a foe or weapon, then mayst thou act so, but not when I am standing thus. 

Thou knowest that with my bow and arrows I am competent to vanquish these worlds with 

1. the gods, 
2. the Asuras, and 
3. men.' 

Hearing these words of Arjuna, Vasudeva replied unto him, saying, 

The form of mine which awaketh from sleep at the end of a thousand years, granteth, upon awakening, excellent boons to persons deserving of them. 

The earth, knowing (on one occasion) that that time had come, asked of me a boon for (her son) Naraka. Hear, O Partha, what that boon was. Possessed of the Vaishnava weapon, let my son become incapable of being slain by the gods and the Asuras. It behoveth thee to grant me that weapon. 

Hearing this prayer, I then gave, in days of old, the supreme and infallible Vaishnava weapon to the Earth's son. 

I said also at that time these words, 

'O Earth, let this weapon be infallible for the protection of Naraka. None will be able to slay him. Protected by this weapon, thy son 

1. will always, 
2. in all the worlds, 
3. be invincible and 
4. crush all hostile hosts.' Saying, So be it! the intelligent goddess went away, her wishes fulfilled. 

And Naraka also became invincible and always scorched his foes. It was from Naraka, O Partha, that the ruler of the Pragjyotishas got this weapon of mine. There is none, in all the world, O sire, including even Indra and Rudra, who is unslayable by this weapon. It was for thy sake, therefore, that I baffled it, violating my promise. 

http://www.sacred-texts.com/hin/m07/m07027.htm