Shiva Purana
मूर्तिं कृत्वा महाविष्णुं सदाशिष्णुमथापि वा ॥ वैष्णवैः पूजितो नित्यं मूर्तित्रयमयासने ॥ १३२ ॥
Or you may make an idol of Lord Viṣṇu or Lord Sadashiṣṇu. He is worshiped by the Vaishnavas daily in the three idols on the seat.
english translation
mUrtiM kRtvA mahAviSNuM sadAziSNumathApi vA ॥ vaiSNavaiH pUjito nityaM mUrtitrayamayAsane ॥ 132 ॥
hk transliteration by Sanscript