Shiva Purana
एकाक्षरादुकाराख्याद्द्विधा विष्णुरुदीर्यते ॥ एकाक्षरान्मकाराख्याच्छिवो रुद्र उदाहृतः ॥ ४६ ॥
Viṣṇu is uttered in two distinct forms, known as the one-syllable Ukāra. From the one syllable makara Shiva is represented as Rudra.
english translation
ekAkSarAdukArAkhyAddvidhA viSNurudIryate ॥ ekAkSarAnmakArAkhyAcchivo rudra udAhRtaH ॥ 46 ॥
hk transliteration by Sanscript