Shiva Purana

siva.sh/siva-purana/kotirudra-samhita/19/3

एवं पूजयतोश्शंभुं तयोर्विष्ण्ववतारयोः ।। चिरकालो व्यतीताय शैवयोर्धर्मपुत्रयोः ।। ३ ।।

sanskrit

A long time elapsed while these two incarnations of Viṣṇu, the spiritual sons of Śiva, performed the worship of Śiva.

english translation

evaM pUjayatozzaMbhuM tayorviSNvavatArayoH || cirakAlo vyatItAya zaivayordharmaputrayoH || 3 ||

hk transliteration by Sanscript