Mbh 12.54.2

"Vaisampayana said, 'When Bhishma that chief of the Kurus, lay on his bed of arrows, many Rishis and Siddhas, O king, headed by Narada, came to that spot. The unslain remnant of the (assembled) kings with Yudhishthira at their head, and Dhritarashtra and Krishna and Bhima and Arjuna and the twins also came there. Those high-souled persons, approaching the grandsire of the Bharatas who looked like the Sun himself dropped from the firmament, indulged in lamentations for him. Then Narada of godlike features reflecting for a short while, addressed all the Pandavas and the unslain remnant of the kings saying, "The time, I think, has come for you to question Bhishma (on subject of morality and religion), for Ganga's son is about to expire like the Sun that is on the point of setting. He is about to cast off his life-breaths. Do you all, therefore, solicit him to discourse to you? He is acquainted with the varied duties of all the four orders. Old in years, after abandoning his body he will obtain high regions of bliss. Solicit him, therefore, without delay, to clear the doubts that exist in your minds." Thus addressed by Narada, those princes approached Bhishma, but unable to ask him anything, looked at one another. Then Yudhishthira the son of Pandu, addressing Hrishikesa said, "There is no one else than Devaki's son that can question the grandsire. O foremost one of Yadu's race, do thou, therefore, O slayer of Madhu, speak first. Thou, O sire, art the foremost of us all and thou art conversant with every duty and practice." Thus addressed by the son of Pandu, the illustrious Kesava of unfading glory, approaching the unconquerable Bhishma, spoke unto him as follows.'