Matsyapurana 111.14

111.14

prajāpateridaṃ kṣetraṃ prayāgamiti viśrutam
etatpuṇyaṃ pavitraṃ vai prayāgaṃ ca yudhiṣṭhira
svarājyaṃ kuru rājendra bhrātṛbhiḥ sahito 'nagha //

O Yudhiṣṭhira! this Prayâga is most sacred. Now you should rule over your empire, along with your brothers, after being cleansed of all your sins.—15.

King! Brahmâ and other Devas have created the universe by placing themselves under the protection of Prayâga. Prajâpati Indra-kṣetra is known as Prayâga.—14.