Joel 2

There are many references in the scriptures to the Great and Terrible day of the Lord. This is just one.

Conspiracy Rising Ref 5

11. And the LORD shall utter his voice before his army: for his camp is very great: for he is strong that executeth his word: for the day of the LORD is great and very terrible; and who can abide it?

http://biblehub.com/joel/2-11.htm