Matsyapurana 106.30

106.30

pūrvapārśve tu gaṅgāyās triṣu lokeṣu bhārata
kūpaṃ caiva tu sāmudraṃ pratiṣṭhānaṃ ca viśrutam //

On the eastern bank of the Ganges, there is a well, by the name of Samudra-Kûpa, and the place Pratiṣṭhâna (modern Jhusi) which is renowned in the three worlds. If one resides there for three nights, observing sexual purity and keeping himself dispassionate, he is freed from all his sins and gets the merit of the performance of Aśvamedha sacrifice.—30-31.