In the first chapter of the Gospel of John, the following account of John the Baptist's introduction of Jesus is given:
29 The next day he saw Jesus coming toward him, and said, “Behold, the Lamb of God, who takes away the sin of the world! 30 This is he of whom I said, ‘After me comes a man who ranks before me, because he was before me.’ 31 I myself did not know him, but for this purpose I came baptizing with water, that he might be revealed to Israel.” 32 And John bore witness: “I saw the Spirit descend from heaven like a dove, and it remained on him. 33 I myself did not know him, but he who sent me to baptize with water said to me, ‘He on whom you see the Spirit descend and remain, this is he who baptizes with the Holy Spirit.’ 34 And I have seen and have borne witness that this is the Son of God.” John 1:29-34
John specifically states that the one who sent him to baptize with water was the one who informed him that he would be able to recognize the one for whom he himself was the predecessor. The indicator would be that John would see the Spirit come down and remain on him.
So, my question is, "Who was it that sent John to baptize with water and who told him how he would be able to recognize Jesus?" Is there anything in church tradition or elsewhere in the Bible that informs us who this was? An angel? God Himself? Another prophet?