Mbh 12.47.2b

O lord of the earth, enquire of him about the four branches of knowledge (in respect of morality, profit, pleasure and salvation), about the sacrifices and the rites laid down for the four orders, about the four modes of life, and about the kingly duties in full. When Bhishma, that foremost one of Kuru's race, will disappear from the world, every kind of knowledge will disappear with him. It is for this that I urge thee (to go to him now)." Hearing these beneficial words of high import from Vasudeva, the righteous Yudhishthira, with voice choked in tears, answered Janardana, saying, "What thou hast said, O Madhava, about the eminence of Bhishma, is perfectly true. I have not the slightest doubt regarding it. Indeed, I had heard of the high blessedness, as also the greatness, of the illustrious Bhishma from high-souled Brahmanas discoursing upon it. Thou, O slayer of foes, art the Creator of all the worlds. There cannot, therefore, O delighter of the Yadavas, be the slightest doubt in what thou sayest. If thy heart be inclined to show grace, O Madhava, then we shall go unto Bhishma with thyself at our head. When the divine Surya shall have turned towards the north, Bhishma will leave (this world), for those regions of bliss that he has won. That descendant of Kuru's race, therefore, O mighty-armed one, deserves to have a sight of thee. (If thou grantest my prayer), Bhishma will then obtain a sight of thee that art the first of Gods, of thee that art destructible and indestructible. Indeed, O lord, thou it is that art the vast receptacle of Brahma."'