Shiva Purana
एवं त्रिधा विभिन्नत्वाद्ब्रह्मा त्रिगुण उच्यते ॥ चतुर्धा प्रविभक्तत्वाच्चातुर्व्यूहः प्रकीर्तितः ॥ २९ ॥
Since he is divided into three he is called Triguṇa. Since he has split himself into four he is glorified as Caturvyūha.
english translation
evaM tridhA vibhinnatvAdbrahmA triguNa ucyate ॥ caturdhA pravibhaktatvAccAturvyUhaH prakIrtitaH ॥ 29 ॥
hk transliteration by Sanscript