Shiva Purana
एतद्द्वयं पराशक्तेः प्रथमं स्पंदतां गतम्॥ एतामेव परां शक्तिं श्वेताश्वतरशाखिनः ॥ ४८ ॥
These two have become the first vibrations of the Supreme Power. This is the supreme power of the white horse branches.
english translation
etaddvayaM parAzakteH prathamaM spaMdatAM gatam॥ etAmeva parAM zaktiM zvetAzvatarazAkhinaH ॥ 48 ॥
hk transliteration by Sanscript