12. The Pentecost, too, we observe, that is, the fiftieth day from the passion and resurrection of the Lord, for on that day He sent to us the Holy Paraclete whom He had promised; as was prefigured in the Jewish passover, for on the fiftieth day after the slaying of the lamb, Moses on the mount received the law written with the finger of God.3 If you read the Gospel, you will see that the Spirit is there called the finger of God.4 Remarkable events which happened on certain days are annually commemorated
Augustine, Reply to Faustus 32.12