In the NKJV, Matthew 27:9-10 reads like this: “Then was fulfilled what was spoken by Jeremiah the prophet, saying, And they took the thirty pieces of silver, the value of Him who was priced, whom they of the children of Israel priced, and gave them for the potter's field, as the LORD directed me.” The difficulty comes when we try to find this material in our canonical Jeremiah. Cross-references send us to Jeremiah 32:6-9, or 18:1-4, or 19:1-3, but upon inspection they must do not match. In Zechariah 11:12-13 we find a general approximation, but it is not precise—and of course Zechariah is not Jeremiah. Evidently there are Hebrew manuscripts that begin the scroll containing the prophets (major and minor) with Jeremiah, and it has been argued that Matthew used ‘Jeremiah’ to refer to the contents of the entire scroll. I suppose that could be a possibility, but I prefer to appeal to Daniel 9:2. “In the first year of his reign [Darius] I, Daniel, understood by the books the number of the years specified by the word of the LORD through Jeremiah the prophet…” Note that ‘books’ is plural. Why should any of us assume that men like Jeremiah, or Isaiah, wrote only what is in our canon? (I myself have written a great deal that has never been published.) Daniel clearly wrote ‘books’, presumably referring to Jeremiah. I conclude that such extra-canonical books were still known in Matthew's day, and that he refers to one of them. I am aware that the distinction cannot be insisted upon, but Matthew did use ‘spoken’ rather than ‘written’.