Shiva Purana
ततस्स शंकरश्शर्वस्सत्यं कर्तुं स्वकं वचः ॥ सुरभ्यां कश्यपाज्जज्ञे एकादशस्वरूपवान् ॥ २४ ॥
Then, in order to keep his promise Śiva was born of Surabhi assuming eleven forms.
english translation
tatassa zaMkarazzarvassatyaM kartuM svakaM vacaH ॥ surabhyAM kazyapAjjajJe ekAdazasvarUpavAn ॥ 24 ॥
hk transliteration by Sanscript