Matthew 3:3
For this is he that was spoken of by the prophet Esaias, saying, The voice of one crying in the wilderness, Prepare ye the way of the Lord, make his paths straight.
Cross-reference
Matthew 11:10 quotes Malachi 3:1 about a messenger preparing the way, same role for John the Baptist as in Isaiah 40:3.
Isaiah 40:3 is the prophecy Matthew directly quotes here — 'A voice crying in the wilderness, prepare the way of the Lord'.
Malachi 3:1 prophesies a messenger preparing the way for the Lord — John the Baptist fulfills this alongside the Isaiah quote here.
Mark 1:3 also quotes Isaiah 40:3 to describe John the Baptist — the same OT reference applied to John's ministry.
Luke 1:17 describes John's mission to prepare a people for the Lord — the same preparatory role depicted in the Isaiah quote here.
Luke 1:76 repeats the 'prepare his ways' language from Isaiah 40:3, directly identifying John as the forerunner.
Luke 3:3-6 also cites Isaiah 40:3-5 about John preparing the way — the same prophecy applied to John in all Synoptics.
In John 1:23, John the Baptist himself says 'I am the voice crying in the wilderness' — directly quoting Isaiah 40:3.
Luke 3:4 records the same Isaiah citation about John preparing the way — a synoptic parallel account.
John 3:28 has John the Baptist stating he was sent ahead of the Messiah, echoing the 'prepare the way' role.