Ambrose of Milan
Catena Aurea · Lukasevangelium 1
And Zacharias said unto the angel, Whereby shall I know this? for I am an old man, and my wife well stricken in years. And the angel answering said unto him, I am Gabriel, that stand in the presence of God; and am sent to speak unto thee, and to shew thee these glad tidings. And, behold, thou shalt be dumb, and not able to speak, until the day that these things shall be performed, because thou believest not my words, which shall be fulfilled in their season. And the people waited for Zacharias, and marvelled that he tarried so long in the temple. And when he came out, he could not speak unto them: and they perceived that he had seen a vision in the temple: for he beckoned unto them and remained speechless.
But a nod is a certain action of the body, without speech endeavouring to declare the will, yet not expressing it.