In Epistle LXXIII, Cyprian writes to Pompey about heretics and baptism. In this letter, he also mentions the beauty of a teachable spirit (cf. 2 Tim. 2.24), which heretics generally do not have. I love these lines.
“Now he is teachable who is meek and gentle to the patience of learning. For it behoves a bishop not only to teach, but also to learn; because he also teaches better who daily increases and advances by learning better.”
Found on page 389 of the Ante-Nicene Fathers, volume 5. By the way, I saw that CBD has many of these individual volumes on sale for around three bucks. Go there and get volume 5 if you want to read Cyprian’s excellent letters and treatises.