Who said "The war within ourselves is the hardest to fight."?

This quote is attributed to The Flash.

The war within ourselves is the hardest to fight. - The Flash

"The war within ourselves is the hardest to fight."

The Flash War

"My name is Barry Allen, and I am the fastest man alive."

"You can't save everyone. Sometimes you have to let people go."

"I'm fighting so that no one else has to suffer like I did."

"Life doesn't give you second chances. So I'm making my own."

"Some battles are worth fighting."

"Sometimes you have to become the monster to stop the monsters."

"Skynet sent me back through time to kill you."

"War teaches us the value of peace."