Shiva Purana
ओङ्कारः परमेशानो धृतः शम्भो परात्मनः ॥ अवतारश्चतुर्थो हि भक्ताभीष्टफलप्रदः ॥ १८ ॥
The fourth incarnation of Śiva the supreme soul, the great lord in Oṃkāra Māndhātā is a bestower of the desires of his devotees.
english translation
oGkAraH paramezAno dhRtaH zambho parAtmanaH ॥ avatArazcaturtho hi bhaktAbhISTaphalapradaH ॥ 18 ॥
hk transliteration by Sanscript