Titus

"For the overseer must be above reproach as God’s steward, not self-willed, not quick-tempered, not addicted to wine, not pugnacious (i.e., quick-tempered), not fond of sordid gain" (Titus 1:7 NASB1995).

In this passage, Paul (Titus 1:1) speaks on how leadership in the church should act. In particular, he notes they must be above reproach, or in some translations, "blameless" (c.f. ASV, CSB, & KJV). Donatists, those who believe that to serve God, you must be perfect, tend to use this passage to show that their leaders must be perfect. The problem with this interpretation is that it misunderstands both the actual Greek. The word here for "above reproach" is "ἀνέγκλητον". 

The idea here is as the ESV Study Bible explains, "there should be no legitimate accusation that could be brought against the elder ... his life should be seen as worthy of imitation" (Crossway 2348, c.f. Gill). Paul here does not mean that leaders must be perfect, as none can be perfect but God (Romans 3:23), but that they should act in a manner that is holy so that the congregation should be able to imitate.