As Kaurawas were losing the battle of Mahabharata, Duryodhana approached Bhisma one night and accused him of not fighting the Mahabharata war to his full strength because of his affection for Pandavas. Bhisma greatly angered, immediately picked up 5 golden arrows and chanted mantras declaring tomorrow he will kill 5 Pandavas with the 5 golden arrows. Duryodhana not having faith in his words asked Bhishma to give custody of 5 golden arrows saying that he will keep them and will return the next morning.
long back before the Mahabharata war, Pandavas were living in exile in a forest. Duryodhana placed his camp on the opposite side of the pond where Pandavas were staying. Once while Duryodhana was taking bath in that pond, the heavenly prince Gandharvas also came down. Duryodhana picked a fight with them only to be defeated and captured. Arjuna saved Duryodhana and set him free. Duryodhana was ashamed but being a Kshatriya, told Arjuna to ask for a boon. Arjuna replied he would ask for the honor gift later when he needed it.
It was during that night of Mahabharata war when Krishna reminded Arjuna of his unsatisfied boon and told him to go to Duryodhana and ask for 5 golden arrows. When Arjuna asked for the arrows Duryodhana was shocked but being a kshatriya and bound by his promise he had to honor his words. He asked who told you about golden arrows, Arjuna replied who else other than Lord Krishna. Duryodhana again went to Bhisma and requested for another five golden arrows. To this Bhisma laughed and replied that is not possible.