Adam Clarke on Mark 1:2

As it is written in the prophets - Rather, As it is written by Isaiah the prophet. I think this reading should be adopted, instead of that in the common text. It is the reading of the Codex Bezae, Vatican, and several other MSS. of great repute. It is found also in the Syriac, Persic, Coptic, Armenian, Gothic, Vulgate, and Itala versions, and in several of the fathers. As this prophecy is found both in Isaiah and Malachi, probably the reading was changed to τοις προφηταις, the prophets, that it might comprehend both. In one of Asseman's Syriac copies, both Isaiah and Malachi are mentioned. See all the authorities in Griesbach, 2d edit.; and see the parallel place in Matthew, Mat 3:3, where the Prophet Isaiah is mentioned, which seems fully to establish the authority of this reading.