1 Thessalonians 3:4-5

For even when we were with you, we warned you plainly in advance that we were going to experience persecution; and so, as you know, it has come to pass. For this reason, when I could no longer endure the suspense, I sent someone to find out about your faith [how you were holding up under pressure], for fear that somehow the tempter had tempted you and our work [among you] would prove to be ineffective.