the mouth of the Lord has spoken it
Isaiah 40:3 (KJV) The voice of him that crieth in the wilderness, Prepare ye the way of the Lord, make straight in the desert a highway for our God.
4 Every valley shall be exalted, and every mountain and hill shall be made low: and the crooked shall be made straight, and the rough places plain:
5 And the glory of the Lord shall be revealed, and all flesh shall see it together: for the mouth of the Lord hath spoken it.
Luke 3:2 Annas and Caiaphas being the high priests, the word of God came unto John the son of Zacharias in the wilderness.
3 And he came into all the country about Jordan, preaching the baptism of repentance for the remission of sins;
4 As it is written in the book of the words of Esaias the prophet, saying, The voice of one crying in the wilderness, Prepare ye the way of the Lord, make his paths straight.
5 Every valley shall be filled, and every mountain and hill shall be brought low; and the crooked shall be made straight, and the rough ways shall be made smooth;