Shiva Purana

siva.sh/siva-purana/rudra-samhita/8/17

एकाक्षरान्मकाराख्याद्भगवान्नीललोहितः ।। सर्गकर्ता त्वकाराख्यो ह्युकाराख्यस्तु मोहकः ।।१७।।

sanskrit

The single syllable “M” is the source of Rudra. The creator is expressed by the letter “A”. The enchanter is expressed by the letter “U”.

english translation

ekAkSarAnmakArAkhyAdbhagavAnnIlalohitaH || sargakartA tvakArAkhyo hyukArAkhyastu mohakaH ||17||

hk transliteration by Sanscript