Ibn Al-Nadim said this quote

“ I have read in some of the old histories that in early times the Greeks did not know how to write until two men, one of whom was called Cadmus (Qatmus) and the other Aghanūn, came from Egypt bringing sixteen letters with which the Greeks wrote. Then one of these two men derived four other letters, also used for writing. Later, another man named Simonides (Simūnidus) derived four additional ones, making twenty-four. It was in those days that Socrates (Suqrātīs) appeared ”