Theodoret's account of Cerdon is to this effect: "He was in the time of tie first Antonius. He taught that there is one God, the Father of our Lord Jesus Christ, unknown to the prophets; another, the Maker of the universe, the giver of the Mosaic law; and this last is just, the other good. For he in the law orders 'that an eye should be given for an eye, and a tooth for a tooth;' but the good God in the Gospels commands that 'to him who smiteth thee on the right cheek, turn the other also;' and that to him who would take away thy coat, thou shouldest give thy cloak also. He in the law directs to love a friend and hate an enemy; but the other, to love even our enemies. 'Not observing,' says Theodoret, 'that in the law it is directed that if a man meet his enemy's ox going astray, he should bring him back; and not forbear to help his beast when Iving under his burden;' and that he who, according to him, is alone good, threatens 'hell-fire to him who calls his brother fool;' and showing himself to be just, said, 'With what measure ye mete, it shall be meted to you again.' " [Nathaniel Lardner the Works of p. 589]
Finally, there is Theodoret of Cyrus, who provides two antitheses in connection with Marcion (Haer. fab. com. I.24. Technically, Theodoret attributes these antitheses to Marcion’s teacher Cerdo, however, there can be no doubt that we are dealing with a re-projection of Marcion’s theology onto Cerdo here, cf. Chapter II): the first is the contrast between the Law’s demand “an eye for an eye” and Christ’s command to turn the other cheek to anyone who hits the right cheek, the second is the opposition between the Law’s demand to love one’s friends and to hate one’s enemies compared to Christ’s command to love one’s enemies also. The fact that Theodoret’s Haereticarum Fabularum Compendium forms a very late source for the analysis of Marcionism (ca. 452/453) makes it all the more striking that the two antitheses which the bishop of Cyrus mentions are also to be found in similar form in the Adamantius-Dialogue and in Tertullian (see above). We can also see once more that the original Marcionite form of these antitheses probably consisted of rather precise statements from both the Old Testament and the Gospel. [Sebastian Moll Marcion p. 156 - 157]Again, keep in mind that Irenaeus's specific claim is that Marcion adapted a pre-existent understanding developed by a certain 'Cerdo' by Marcion according to one gospel and then Luke was deliberately falsified according to these principles. It gets sillier and sillier the more you look at the evidence. Luke was clearly post-Marcion.