The Prescription Against Heretics by Tertullian
Chapter XII.--A Proper Seeking After Divine Knowledge, Which Will Never Be Out of Place or Excessive, is Always Within the Rule of Faith.
As for us, although we must still seek, and that always, yet where ought our search to be made? Amongst the heretics, where all things are foreign and opposed to our own verity, and to whom we are forbidden to draw near? What slave looks for food from a stranger, not to say an enemy of his master? What soldier expects to get bounty and pay from kings who are unallied, I might almost say hostile -- unless forsooth he be a deserter, and a runaway, and a rebel? Even that old woman searched for the piece of silver within her own house. It was also at his neighbour's door that the persevering assailant kept knocking. Nor was it to a hostile judge, although a severe one, that the widow made her appeal. No man gets instruction from that which tends to destruction. No man receives illumination from a quarter where all is darkness. Let our |seeking,| therefore be in that which is our own, and from those who are our own: and concerning that which is our own, -- that, and only that, which can become an object of inquiry without impairing the rule of faith.