1 Timothy 3:9

holding the mystery of the faith with a pure conscience.

Surrounding context

3:8 Likewise deacons must be reverent, not double-tongued, not given to much wine, not greedy for money,

3:9 holding the mystery of the faith with a pure conscience.

3:10 But let these also first be tested; then let them serve as deacons, being found blameless.

Translation and sources