I've finally got hold of my Kindle notes, which Amazon makes it ridiculously hard to copy and paste.
"Now, on the contrary, much knowledge is traced on paper, but little is engraved in the soul. A man is certain that he can find information at a moment's notice when he wants it. He therefore suffers it to fade from his mind. Such a man cannot in strictness be said to know anything. He has the show without the reality of wisdom. These opinions Plato has put into the mouth of an ancient king of Egypt."
But Macaulay had little tolerance for them, and he would probably have just as little with the modern version.