Shiva Purana

siva.sh/siva-purana/saturda-samhita/33/64

इति प्रोक्तस्तु ते तात ब्रह्मचारि स्वरूपकः ।। शिवावतारो हि मया शिवाभावपरीक्षकः ।। ६४ ।।

sanskrit

My dear son, when I had thus spoken to you, I was a celibate and a self-realized being. . I have incarnated Lord Śiva as a test of the absence of Lord Śiva.

english translation

iti proktastu te tAta brahmacAri svarUpakaH || zivAvatAro hi mayA zivAbhAvaparIkSakaH || 64 ||

hk transliteration by Sanscript