In the third month, when the children of Israel were gone forth out of the land of Egypt, the same day came they into the wilderness of Sinai.
All Commentaries on Exodus 19:1 Go To Exodus 19
Augustine of Hippo
AD 430
But the fiftyday period is also praised in Scripture, not only in the Gospel, because the Holy Spirit came on the fiftieth day, but even in the Old Testament. Therein fifty days are numbered from the celebration of the pasch by the killing of a lamb to the day on which the law was given on Mt. Sinai to the servant of God, Moses.