"For," says he, "I have begotten you through the gospel. Ye are my children, of whom I travail again in birth." (1 Corinthians 4:15; Galatians 4:19) [Tertullian Against Marcion 5.8.6]
For he says, My little children, of whom I travail in birth again until Christ be formed in you (Galatians 4:19) and again, In Christ Jesus I have begotten you through the Gospel. (1 Corinthians 4:15) [Methodius Banquet of the Ten Virgins 9]
That is why Paul says in his letter to Galatians, "My little children, I am going through the pains of childbirth with you a second time until Christ is formed in you" (Galatians 4:19) Yet again in writing to the Corinthians he says, "You may have thousands of tutors in Christ but only one father. I am your father in Christ through the gospel." (1 Corinthians 4:15) [Clement Stromata 3.99.3]
I think I could literally come up with at least fifty - possibly a hundred - parallels like this between the writings of Clement and Methodius. Doesn't that make a strong argument that there was a common Apostolikon and that their writings were subsequently corrupted? I can't believe that people are going to argue that the parallels between patterns of scriptural citation happen to be mere 'coincidence.' I am convinced Tertullian is actually preserving the original 'centonized' Apostolikon of the Marcionites here, a canon shared with Clement and Methodius.