Anshuman, the grandson of Sagara came to know of the fate of his elders and asked the sage for forgiveness. But water was needed for the last rites. The sage said that his elders could be brought back to life, if the sacred waters of the celestial Ganges could be made to flow over their ashes. Neither Anshuman nor Dilipa could do the needful in the matter. The task was ultimately accomplished by Bhagiratha, the son of Dilipa.
He propitiated both Brahma and Shiva and brought the Ganges to the earth. Thence he conducted the waters of Patala, where the ashes of the sixty thousand sons of Sagara were watered and restored them back to life. They were purified by the sacred waters of all their sins and then ascended to heaven. See : Ganga and Jaharnavi (Jahnavi)
References :
1. Kohli,Surindar Singh ed, Dictionary of Mythological References in Guru Granth Sahib, 1993