Shiva Purana
विष्णुस्तत्रैव सुष्वाप प्रकृत्या स्वस्त्रिया सह ॥ तन्नाभिकमलाज्जातो ब्रह्मा शंकरशासनात् ॥ १६ ॥
Viṣṇu slept there itself along with his consort Prakṛti. At the behest of Śiva, Brahmā was born of his umbilical lotus.
english translation
viSNustatraiva suSvApa prakRtyA svastriyA saha ॥ tannAbhikamalAjjAto brahmA zaMkarazAsanAt ॥ 16 ॥
hk transliteration by Sanscript