Vishnupurana 2.8.109

2.8.109

vāmapādāmbujāṅguṣṭhanakhasrotovinirgatām
viṣṇor bibharti yāṃ bhaktyā śirasāharniśaṃ dhruvaḥ //

From that third region of the atmosphere, or seat of Vishńu, proceeds the stream that washes away all sin, the river Gangá, embrowned with the unguents of the nymphs of heaven, who have sported in her waters. Having her source in the nail of the great toe of Vishńu's left foot, Dhruva receives her, and sustains her day and night devoutly on his head; and thence the seven Rishis practise the exercises of austerity in her waters, wreathing their braided locks with her waves. The orb of the moon, encompassed by her accumulated current, derives augmented lustre from her contact. Falling from on high, as she issues from the moon; she alights on the summit of Meru, and thence flows to the four quarters of the earth, for its purification. The Śítá, Alakanandá, Chakshu, and Bhadrá are four branches of but one river, divided according to the regions towards which it proceeds. The branch that is known as the Alakanandá was borne affectionately by Mahádeva, upon his head, for more than a hundred years, and was the river which raised to heaven the sinful sons of Sagara, by washing their ashes. The offences of any man who bathes in this river are immediately expiated, and unprecedented virtue is engendered. Its waters, offered by sons to their ancestors in faith for three years, yield to the latter rarely attainable gratification. Men of the twice-born orders, who offer sacrifice in this river to the lord of sacrifice, Purushottama, obtain whatever they desire, either here or in heaven. Saints who are purified from all soil by bathing in its waters, and whose minds are intent on Keśava, acquire thereby final liberation. This sacred stream, heard of, desired, seen, touched, bathed in, or hymned, day by day, sanctifies all beings; and those who, even at a distance of a hundred leagues, exclaim "Gangá, Gangá," atone for the sins committed during three previous lives. The place whence this river proceeds, for the purification of the three worlds, is the third division of the celestial regions, the seat of Vishńu.