In Harper Lee's To Kill a Mockingbird, aside from all of the various places in which the Finch children are insulted by individuals who call Atticus a "nigger-lover"--such as by Cecil Jacobs in Chapter 9, by the Finches' cousin Francis in Chapter 9, and by Mrs. Dubose in Chapter 11--some of the most noteworthy racist remarks can be found in Chapter 24, during the meeting of Aunt Alexandra's missionary circle in the Finches' home.
During the meeting, the women had been discussing an African tribe that very few missionaries had attended to. Mrs. Merriweather calls the area of Africa a land of "nothing but sin and squalor." While we don't hear Gertrude's comment in reply, we can assume Gertrude noted that Maycomb is full of just as much "sin and squalor," since African Americans like Tom Robinson commit such heinous crimes and corrupt the rest of the African-American society. We can assume what Gertrude's remark was based on Mrs. Merriweathers very racist reply:
Oh that. Well, I always say forgive and forget, forgive and forget. Thing that church ought to do is help her lead a Christian life for those children from here on out. (Ch. 24)
The remark is racist because it assumes Tom Robinson's wife, Helen, has done something that requires being forgiven and forgotten. In other words, it assumes that just because Mr. Robinson was found guilty by a jury, despite all evidence pointing to the opposite, Mrs. Robinson must be equally guilty of sinful behavior due to Mr. Robinson's influence. Hence, Mrs. Merriweather is assuming Mrs. Robinson isn't truly a Christian, despite the Robinson's devoted attendance of church. Mrs. Merriweather makes this assumption based on the racist belief that all African Americans are evil by nature.
The above racist belief is revealed by Mrs. Farrow, who responds to Mrs. Merriweather:
... looks like we're fighting a losing battle, a losing battle. ... We can educate 'em till we're blue in the face, we can try till we drop to make Christians out of 'em, but there's no lady safe in her bed these nights. (Ch. 24)
As we can see, Mrs. Farrow's racist remark assumes that African Americans cannot be educated and cannot be taught Christianity, all because they are evil by nature even though, ironically, Maycomb's African-American citizens are far more humble Christians than those in Aunt Alexandra's missionary circle.
Page numbers will vary per version of the book; however, the passages in question are located in the middle of Chapter 24, approximately 5 to 6 pages from the beginning of the chapter.