Mahabharata 13.26.35

13.26.35

daśa tīrthasahasrāṇi tisraḥ koṭyastathāparāḥ |
samāgacchanti māghyāṃ tu prayāge bharatarṣabha || 35 ||

Bathing in the confluence of the Ganga and the Yamuna as also at the tirtha in the Kalanjara mountains and offering every day oblations of water to the Pitris for a full month, one acquires the merit that attaches to ten Horse-sacrifices. Bathing in the Shashthi lake one acquires merit much greater than what is attached to the gift of food. Ten thousand tirthas and thirsty millions of other tirthas come to Prayaga (the confluence of Ganga and Yamuna), O chief of Bharata's race in the month of Magha. He who bathes in Prayaga, with a restrained soul and observing rigid vows the while, in the month of Magha, becomes cleansed of all his sins, O chief of Bharata's race, and attains to heaven. Bathing in the tirtha that is sacred to the Maruts, as also in that which is situate in the retreat of the Pitris, and also in that which is known by the name of Vaivaswata, one becomes cleansed of all one's sins and becomes as pure and sanctified as a tirtha. Repairing to Brahmasaras as also to the Bhagirathi and bathing there and offering oblations to the Pitris every day for a full month, abstaining from food all the while, one is sure to attain to the region of Soma, Bathing in Utpataka and then in Ashtavakra and offering oblations of water to the Pitris every day for twelve days in succession, abstaining the while from food, one acquires the merits of a Horse-sacrifice.