And thus preaching through countries and cities, they appointed the first fruits [of their labors], having first proved them by the Spirit, to be bishops and deacons of those who should afterwards believe. Nor was this any new thing, since indeed many ages before it was written concerning bishops and deacons…. Our apostles also knew, through our Lord Jesus Christ, that there would be strife on account of the office of the episcopate. For this reason, therefore, since they had obtained a perfect foreknowledge of this, they appointed those [ministers] already mentioned, and afterwards gave instructions that when these should fall asleep, other approved men should succeed them in their ministry. – Letter to the Corinthians 42:4–5; 44:1–2 (70 A.D).

Clement of Rome