Shiva Purana
अकारश्च उकारश्च मकारश्च ततः परम् । बिंदुनादयुतं तद्धि शब्दकालकलान्वितम् १३ ।
The long one is present in the heart of the Yogins alone—separately in the form of “A” syllable, “U” syllable, “M” syllable, Bindu and Nāda.
english translation
akArazca ukArazca makArazca tataH param । biMdunAdayutaM taddhi zabdakAlakalAnvitam 13 ।
hk transliteration by Sanscript