Agni Purana (Jyotisha Selections) · by Vyasa
Chapter 2 · War Astrology: Yogas, Nakshatras
युद्धजयार्णवः (योगाः नक्षत्राणि)
जातो नाद उकारस्तु नदते हृदि संस्थितः ।अर्धचन्द्र इकारस्तु मोक्षमार्गस्य बोधकः ॥ ९ ॥
In the full Agni Purana this is chapter 124, verse 9.
Then the sound was born, the letter u. It sounds, sitting in the heart. The half-moon is the letter i. It shows the path to liberation.
Simple meaning: The sound u sits in the heart. The half-moon i shows the path to liberation.
अकारोऽव्यक्त उत्पन्नो भोगमोक्षप्रदः परः ।
The letter a is unseen and beyond, and gives enjoyment and liberation. It holds earth and the part called Nivritti.
गन्धो न बीजः प्राणाख्य इडा शक्तिः स्थिरा स्मृता ।
The vowels a and i are matched with senses, seed letters, breaths, and the left and right breath.
क्रूरा शक्तिरीबीजः स्याद्धरवीजोऽग्निरूपवान् ।
Powers and seed letters are named, including cruel Shakti and a fire-like seed.