When did the immutability of God become entrenched in Christian literature?

The immutability of God means God does not change, and it is considered heresy to disagree. However, this concept seems so close to the Greek's idea of perfection, and to conflict with the well-known idea that God became a Man. When did this idea appear in the writings of the church fathers, and when did it become enshrined by the church councils? It does not seem to be in the Apostle's Creed for example.