Shiva Purana
शिवतत्त्वादिभूम्यन्तं शरीरादि घटादि च॥ व्याप्याधितिष्ठति शिवस्तमाद्विष्णुरुदाहृतः॥ १५॥
Śiva is called Viṣṇu because he pervades the principles of Śiva ending with the earth and the bodies, pots etc.
english translation
zivatattvAdibhUmyantaM zarIrAdi ghaTAdi ca॥ vyApyAdhitiSThati zivastamAdviSNurudAhRtaH॥ 15॥
hk transliteration by Sanscript