Shiva Purana

siva.sh/siva-purana/rudra-samhita/183/15

चर्तुं हि शक्यं तु सुरासुरैर्यत्र तादृशं वर्षसहस्रमात्रम् ।। सा पार्वती मंदरपर्वतस्था प्रतीक्ष्यमाणागमनं भवस्य ।। १५ ।।

sanskrit

Śiva performed penance for a thousand years the like of which could not be performed by the gods or Asuras. Pārvatī stayed behind in Mandara mountain awaiting for the return of the lord.

english translation

cartuM hi zakyaM tu surAsurairyatra tAdRzaM varSasahasramAtram || sA pArvatI maMdaraparvatasthA pratIkSyamANAgamanaM bhavasya || 15 ||

hk transliteration by Sanscript