A hero does not exhaust immediately upon proposing a combat. Many people tend to play a little too fast and just exhaust a character right away even though they need to wait to see if there is any responses to the proposal (like Hammer of Justice) that could negate the attack. Only if the proposal is successful will the character exhaust and the combat begin.
The correct sequence of events would be he proposes a combat with his hero, you respond by playing Hammer of Justice, and he responds by exhausting his hero for Blessing of Wisdom.
No quote for you!