Manasara 45.59

45.59

etatpadmāsanaṃ proktaṃ śivaviṣṇvāsanaṃ bhavet
tadeva sopapīṭhe syātpadmakesaramīritam

This is declared as the padmāsana; it should be the seat for Śiva and Viṣṇu; / that same seat on a pedestal (upapīṭha) is called padmakesara.