Bhagavad Gita, Chapter 10, Verse 33

Of letters the letter A am I, and Dvandva of all compounds; I alone am the inexhaustible Time, I the Sustainer (by dispensing fruits of actions) All-formed.

Even the most basic building block of language, a single letter, is claimed here as a real starting point of everything spoken.

Choosing the first letter of the alphabet rather than a whole word or sentence makes the point at its smallest, most foundational scale. Real origin is shown reaching down to language's most basic unit.