Malachi 4:5

4:5 Look, I will send you Elijah the prophet before the great and terrible day of the Lord arrives.

Matthew 11:14

11:14 And if you are willing to accept it, he is Elijah, who is to come.

Matthew 17:10-12

17:10 The disciples asked him, “Why then do the experts in the law say that Elijah must come first?” 17:11 He answered, “Elijah does indeed come first and will restore all things. 17:12 And I tell you that Elijah has already come. Yet they did not recognize him, but did to him whatever they wanted. In the same way, the Son of Man will suffer at their hands.”

Luke 1:17

1:17 And he will go as forerunner before the Lord in the spirit and power of Elijah, to turn the hearts of the fathers back to their children and the disobedient to the wisdom of the just, to make ready for the Lord a people prepared for him.”