Irenaeus on the Ebionites

Adversus Haereses (Book I, Chapter 26)

Those who are called Ebionites agree that the world was made by God; but their opinions with respect to the Lord are similar to those of Cerinthus and Carpocrates. They use the Gospel according to Matthew only, and repudiate the Apostle Paul, maintaining that he was an apostate from the law. As to the prophetical writings, they endeavour to expound them in a somewhat singular manner: they practise circumcision, persevere in the observance of those customs which are enjoined by the law, and are so Judaic in their style of life, that they even adore Jerusalem as if it were the house of God.

Adversus Haereses (Book III, Chapter 21)

God, then, was made man, and the Lord did Himself save us, giving us the token of the Virgin. But not as some allege, among those now presuming to expound the Scripture, [thus:] "Behold, a young woman shall conceive, and bring forth a son," Isaiah 7:14 as Theodotion the Ephesian has interpreted, and Aquila of Pontus, both Jewish proselytes. The Ebionites, following these, assert that He was begotten by Joseph; thus destroying, as far as in them lies, such a marvellous dispensation of God, and setting aside the testimony of the prophets which proceeded from God.

Adversus Haereses (Book V, Chapter 1)

Vain also are the Ebionites, who do not receive by faith into their soul the union of God and man, but who remain in the old leaven of [the natural] birth, and who do not choose to understand that the Holy Ghost came upon Mary, and the power of the Most High did overshadow her.