Shiva Purana
तस्मादेकाक्षरन्देवं शिवं परमकारणम् ॥ उपासते यतिश्रेष्ठा हृदयाम्भोजमध्यगम् ॥ ६३ ॥
Hence good ascetics worship Śiva the single-syllabled lord who being the cause of the universe is stationed in the lotus of the heart.
english translation
tasmAdekAkSarandevaM zivaM paramakAraNam ॥ upAsate yatizreSThA hRdayAmbhojamadhyagam ॥ 63 ॥
hk transliteration by Sanscript