Origen, on Exod 19:16

“And now the third day was come, and the morning appeared: and behold thunders began to be heard, and lightning to flash, and a very thick cloud to cover the mount, and the noise of the trumpet sounded exceeding loud, and the people that was in the camp, feared.”

“The third day, however, is always applied to mysteries. For when the people had departed from Egypt, they offer sacrifice to God on the third day and are purified on the third day. And the third day is the day of the Lord's resurrection. Many other mysteries also are anticipated in this day.”

Imported from an open dataset — not yet checked against the printed edition.