29 Now, if any one finds a difficulty in the circumstance that this passage is not found in the writings of the prophet Jeremiah, and thinks that damage is thus done to the veracity of the evangelist, let him first take notice of the fact that this ascription of the passage to Jeremiah is not contained in all the codices of the Gospels, and that some of them state simply that it was spoken “by the prophet.” It is possible, therefore, to affirm that those codices deserve rather to be followed which do not contain the name of Jeremiah.
For these words were certainly spoken by a prophet, only that prophet was Zechariah. In this way the supposition is, that those codices are faulty which contain the name of Jeremiah, because they ought either to have given the name of Zechariah or to have mentioned no name at all, as is the case with a certain copy, merely stating that it was spoken “by the prophet, saying,” which prophet would assuredly be understood to be Zechariah. However, let others adopt this method of defence, if they are so minded.
For my part, I am not satisfied with it; and the reason is, that a majority of codices contain the name of Jeremiah, and that those critics who have studied the Gospel with more than usual care in the Greek copies, report that they have found it stand so in the more ancient Greek exemplars. I look also to this further consideration, namely, that there was no reason why this name should have been added [subsequently to the true text], and a corruption thus created; whereas there was certainly an intelligible reason for erasing the name from so many of the codices. For venturesome inexperience might readily have done that, when perplexed with the problem presented by the fact that this passage could not be found in Jeremiah.
Source: The Harmony of the Gospels (New Advent)