Origen

(in Joan. tom. vi. c. 7) Some one will say that John was ignorant that he was Elias; as those say, who maintain, from this passage the doctrine of a second incorporation, as though the soul took up a new body, after leaving its old one. For the Jews, it is said, asking John by the Levites and priests, whether he is Elias, suppose the doctrine of a second body to be already certain; as though it rested upon tradition, and were part of their secret system. To which question, however, John replies, I am not Elias: not being acquainted with his own prior existence. But how is it reasonable to imagine, if John were a prophet enlightened by the Spirit, and had revealed so much concerning the Father, and the Only-Begotten, that he could be so in the dark as to himself, as not to know that his own soul had once belonged to Elias?