Revākhaṇḍa ascribed to the Vāyupurāṇa (RKV) 10.43

10.43

saridbhirbhrājate śreṣṭhā purī śākrī ca bhāskarī /
kecitpañcāgnitapasaḥ kecidapyagnihotriṇaḥ //

the best of rivers shines like the city of Śakra and the city of Bhāskara. / Some practised the asceticism of the five fires, while others maintained the agnihotra fire;