Malachi 4:5 - 6
ESV - 5 Behold, I will send you Elijah the prophet before the great and awesome day of the Lord comes. 6 And he will turn the hearts of fathers to their children and the hearts of children to their fathers, lest I come and strike the land with a decree of utter destruction.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.