Shiva Purana

siva.sh/siva-purana/kotirudra-samhita/22/4

स एव हि द्विधा जातः पुंस्त्रीरूपप्रभेदतः ।। यः पुमान्स शिवः ख्यातः स्त्रीशक्तिस्सा हि कथ्यते ।। ४ ।।

sanskrit

That split itself into two in the male and the female forms. The male is famous as Śiva and the female is known as Śakti.

english translation

sa eva hi dvidhA jAtaH puMstrIrUpaprabhedataH || yaH pumAnsa zivaH khyAtaH strIzaktissA hi kathyate || 4 ||

hk transliteration by Sanscript