Malachi-4:5-nasb,nasb

Luke 1:17 NIV
And he will go on before the Lord, in the spirit and power of Elijah, to turn the hearts of the parents to their children and the disobedient to the wisdom of the righteous—to make ready a people prepared for the Lord.”

Malachi 3:1 NIV
“I will send my messenger, who will prepare the way before me. Then suddenly the Lord you are seeking will come to his temple; the messenger of the covenant, whom you desire, will come,” says the Lord Almighty.

Matthew 17:10-13 NIV
The disciples asked him, “Why then do the teachers of the law say that Elijah must come first?” Jesus replied, “To be sure, Elijah comes and will restore all things. But I tell you, Elijah has already come, and they did not recognize him, but have done to him everything they wished. In the same way the Son of Man is going to suffer at their hands.” Then the disciples understood that he was talking to them about John the Baptist.