Tertullian

And how is it that he enjoins duties which belong to our God, and enjoins them to be offered to none other than our God? Either contend that the devil works with our God, or else let the Paraclete be held to be Satan. But you affirm it is "a human Antichrist: "for by this name heretics are called in John. And how is it that, whoever he is, he has in (the name of) our Christ directed these duties toward our Lord; whereas withal antichrists have (ever) gone forth (professedly teaching) towards God, (but) in opposition to our Christ? On which side, then, do you think the Spirit is confirmed as existing among us; when He commands, or when He approves, what our God has always both commanded and approved? But you again set up boundary-posts to God, as with regard to grace, so with regard to discipline; as with regard to gifts, so, too, with regard to solemnities: so that our observances are supposed to have ceased in like manner as His benefits; and you thus deny that He still continues to impose duties, because, in this case again, "the Law and the prophets (were) until John.

Although we ought to be seeking at all times, where ought we to seek? Among the heretics, where all is foreign and opposed to our truth, with whom we are forbidden to associate?