Acceptance in The Big Book.
 
Question: Where can I find the part about acceptance in The Big Book.
 
Answer: Acceptance was an idea in a personal story introduced in the 3rd edition. It was not part of the original Big Book but an opinion expressed by the man that wrote the story.

The story appears in the Big Book along with dozens of other stories where: "you will find a wide variation in the way each teller approaches and conceives of the Power which is greater than himself. Whether we agree with a particular approach or conception seems to make little difference. Experience has taught us that these are matters about which, for our purpose, we need not be worried. They are questions for each individual to settle for himself."

"On one proposition, however, these men and women are strikingly agreed. Every one of them has gained access to, and believes in, a Power greater than himself. This Power has in each case accomplished the miraculous, the humanly impossible." -Page 50

See page 449 in the 3rd edition or page 417 in the 4th edition.

It says in part:
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.

Use this link to read the story on the AA.org website.
(It opens a PDF file.)

Apart from the story acceptance is not discussed in the same manner in the main text of the Big Book. The sum of what chapters 1-11 have to say on acceptance is as follows:

14:2:1 These were revolutionary and drastic proposals, but the moment I fully accepted them, the effect was electric.

47:3:1 That was great news to us, for we had assumed we could not make use of spiritual principles unless we accepted many things on faith which seemed difficult to believe.

48:2:5 Why this ready acceptance?

80:2:2 While drinking, he accepted a sum of money from a bitterly-hated business rival, giving him no receipt for it.

134:2:6 This may hang on for months, long after their mother has accepted dad's new way of living and thinking.

139:1:3 Without much ado, he accepted the principles and procedure that had helped us.

145:1:3 In fact, he may say almost anything if he has accepted our solution which, as you know, demands rigorous honesty.