Thanks for your question.
This is not a quotation from the Bible. However, the mind is indeed a battlefield in which the inclinations of the flesh war against the righteousness of the spirit of God. Our decision in this battle will decide our destiny. We cannot defeat the flesh on our own; we need to enlist the help that God alone supplies through His beloved son. See Romans chapters 7 and 8 for the Apostle Paul's take on this.
I hope you have found this helpful.
God bless and keep you!