Shiva Purana

siva.sh/siva-purana/saturda-samhita/10/7

सङ्ख्या विशक्यते कर्तुं सुप्राज्ञैर्बहुजन्मभिः ।। शिवावताराणां नैव सत्यं जानीहि मद्वचः ।। ७।।

sanskrit

It is possible to count them in many births by the wise Know that my words are not true of the incarnations of Lord Śiva.

english translation

saGkhyA vizakyate kartuM suprAjJairbahujanmabhiH || zivAvatArANAM naiva satyaM jAnIhi madvacaH || 7||

hk transliteration by Sanscript