From ‘The Prescription Against Heretics’ by Tertullian.
Now the reason of this saying is comprised in three points: in the matter, in the time, in the limit. In the matter, so that you must consider what it is you have to seek; in the time, when you have to seek; in the limit, how long. What you have “to seek,” then, is that which Christ has taught, (and you must go on seeking) of course for such time as you fail to find, —until indeed you find it. But you have succeeded in finding when you have believed. For you would not have believed if you had not found; as neither would you have sought except with a view to find. Your object, therefore, in seeking was to find; and your object in finding was to believe. All further delay for seeking and finding you have prevented by believing. The very fruit of your seeking has determined for you this limit. This boundary has He set for you Himself, who is unwilling that you should believe anything else than what He has taught, or, therefore, even seek for it. If, however, because so many other things have been taught by one and another, we are on that account bound to go on seeking, so long as we are able to find anything, we must (at that rate) be ever seeking, and never believe anything at all. For where shall be the end of seeking? where the stop in believing? where the completion in finding? (Shall it be) with Marcion? But even Valentinus proposes (to us the) maxim, “Seek, and ye shall find.” (Then shall it be) with Valentinus? Well, but Apelles, too, will assail me with the same quotation; Hebion also, and Simon, and all in turn, have no other argument wherewithal to entice me, and draw me over to their side. Thus I shall be nowhere, and still be encountering(that challenge), “Seek, and ye shall find,” precisely as if I had no resting-place; as if (indeed) I had never found that which Christ has taught—that which ought to be sought, that which must needs be believed.