The birth of John [the Baptist] brought the dumbness of Zacharias to an end. For he did not burden his father, when the voice issued forth from silence; but as when not believed it rendered him tongue-tied, so did the voice sounding out clearly set his father free, to whom he had both been announced and born. Now the voice and the burning light were a precursor of the Word and the Light.
Source: Fragments from the Lost Writings of Irenaeus (New Advent)