Shiva Purana
ब्रह्मणः पुत्रकामस्य ध्यायतो मनसा शिवम् ॥ प्रादुर्भूता महानादा विश्वरूपा सरस्वती ॥३२॥
As Brahmā, desirous of sons, meditated on Śiva mentally, Sarasvatī (Goddess of speech) of great sound manifested herself. She was Viśvarūpā (Universe-formed).
english translation
brahmaNaH putrakAmasya dhyAyato manasA zivam ॥ prAdurbhUtA mahAnAdA vizvarUpA sarasvatI ॥32॥
hk transliteration by Sanscript