Shiva Purana
सर्वं तिसृभिरेवेदं मात्राभिर्निखिलं त्रिधा ॥ अभिधाय शिवात्मानं बोधयत्यर्धमात्रया ॥ ३० ॥
Praṇava expresses everything through the three Mātrās in three ways and indicates Śivātman through half a Mātrā.
english translation
sarvaM tisRbhirevedaM mAtrAbhirnikhilaM tridhA ॥ abhidhAya zivAtmAnaM bodhayatyardhamAtrayA ॥ 30 ॥
hk transliteration by Sanscript