Esther 7:9
And Harbonah, one of the chamberlains, said before the king, Behold also, the gallows fifty cubits high, which Haman had made for Mordecai, who had spoken good for the king, standeth in the house of Haman. Then the king said, Hang him thereon.
Haman had erected the gallows for Mordecai, yet that same gallows became the means of his own execution and punishment. The turning of his plan against himself shows that schemes laid against God's people can be defeated and made to return upon the heads of those who devise them. In this reversal lay deliverance for God's people from Haman's decree of destruction.