The often quoted section on acceptance from page 449 in the 3rd edition or page 417 in the 4th edition.

“And acceptance is the answer to all my problems today. When I am disturbed, it is because I find some person, place, thing, or situation-some fact of my life-unacceptable to me, and I can find no serenity until I accept that person, place, thing, or situation as being exactly the way it is supposed to be at this moment. Nothing, absolutely nothing, happens in God’s world by mistake. Until I could accept my alcoholism, I could not stay sober; unless I accept life completely on life’s terms, I cannot be happy. I need to concentrate not so much on what needs to be changed in the world as on what needs to be changed in me and in my attitudes.”

The quote was taken from “ACCEPTANCE WAS THE ANSWER” found in the section They Stopped in Time in the Big Book of Alcoholics Anonymous, and the full text of “ACCEPTANCE WAS THE ANSWER” can be found here on page 407.

What Is Acceptance? By Bill W. appeared in the AA Grapevine in March 1962.
It can be found here,What Is Acceptance? by Bill W.