Arjuna takes a terrible oath.Mahabharata 150

 Krishna advises  Arjuna to stop grieving for his son as he has attained Veera swarga, but Arjuna is still inconsolable. He turns to his brothers and asks, his voice quivering with sadness 'Tell me what happened to Abhimanyu. How is it possible that while highly skilled warriors like you were with him, he was killed? If I had known this, I would not have left him alone in the battle field. If Abhimanyu died right in front of your eyes, can we still claim that you are brave and formidable warriors! It is mainly my fault that I believed in you and left him in your care. You are only capable of talking in a sabha and are incapable of  protecting a mere boy. The arms and armours with you are just  for show!'

With Arjuna in this state, none is able to talk or even look at him, except Yudhisthira and Krishna.  Finally Yudhisthira tells him briefly how it happened. 'We were right behind Abhimanyu, but Saindhava, blessed by a boon by Rudra, stopped all of us from following Abhimanyu. Once he was in, Drona, Kripa, Karna, Ashwathama, Bruhadbala and Kruthavarma surrounded him. He fought valiantly sent hundreds of Rajaputras and Bruhadbala to heaven, then destiny took him away from us, leaving us all desolate. This is what happened.' 

Arjuna is overcome with grief and cries 'Oh my son!' He gnashes his teeth and wrings his hand like a man who is delirious with a high fever. He appears as if he has gone mad and announces, 'Here is my oath! I will kill that Saindhava Jayadratha tomorrow. If he runs away scared and deserts the kaurava army or if he comes and surrenders to either me or Krishna, I will spare him. If not, it is certain that I will kill him. Whoever comes to protect him, whether it is Dronacharya or Kripacharya, I will also kill them. If I am unable to do this, let me be derprived my place in heaven and suffer the misfortune that befalls the killers of their own parents. If the sun sets tomorrow and I have not yet killed him , I will offer myself  as a sacrifice to agni.' . Having said this, Arjuna rotates his bow Gandhiva around him and sounds his conch Devadatta, Krishna sounds his conch Panchajanya supporting his resolve. Soon others followed with drums and musical instruments and loud war-cries.