Shiva Purana

siva.sh/siva-purana/kotirudra-samhita/22/7

महासंशयमापन्नौ प्रकृतिः पुरुषश्च तौ ।। तदा वाणी समुत्पन्ना निर्गुणात्परमात्मनः ।। तपश्चैव प्रकर्तव्यं ततस्सृष्टिरनुत्तमा ।। ७।।

sanskrit

Nature and the soul were in great doubt Then a voice emerged from the transcendental Supreme Soul One should also practice austerities and thereby attain supreme creation.

english translation

mahAsaMzayamApannau prakRtiH puruSazca tau || tadA vANI samutpannA nirguNAtparamAtmanaH || tapazcaiva prakartavyaM tatassRSTiranuttamA || 7||

hk transliteration by Sanscript