Saurapurana 68.1

68.1

prāyaḥ prāntamupoṣyaṃ syāttīrthe devaphalepsubhiḥ
mūlaṃ hi pitṛtuṣṭyarthaṃ pitryaṃ coktaṃ maharṣibhiḥ

Generally, fasting at the edge [of the water] should be done at a sacred ford by those desiring divine fruit; / indeed, what pertains to the ancestors, intended for their satisfaction, has been declared by the great sages to be fundamental.