In William Faulkner's novel Requiem for a Nun, depending on one's edition, Nancy Mannigoe's defense lawyer Gavin Stevens says to Temple, "The past is never dead. It's not even past," on page 73 of Act 1, Scene 3. Stevens says this in response to Temple's statement that "Temple Drake is dead."
What Temple means in saying the above is that she considers her life as a prostitute living in the brothel run by Popeye in Memphis, Tennessee, to be over and done with, to be dead. However, it's this past that connects her to Nancy, an African-American woman whom Temple refers to as a "dope-fiend nigger whore" due to Nancy's known drug addictions and work as a prostitute. Temple had hired Nancy as a nanny and found Nancy to be the only one she could talk to about her past life. Nancy smothered Temple's daughter in an effort to force Temple to give up the idea of abandoning her husband and children to run off with Pete, a man blackmailing Temple with the exposure of letters he has in his possession that Temple wrote to Alabama Red, her lover while she was in the brothel, detailing how much she enjoyed her experiences with Red. If such letters surfaced, they would destroy her current reputation as a wife and mother.
In Act 1, Scene 3, Stevens is talking with both Temple and her husband Gowan in an effort to find out more about Temple's past and how it connects with Nancy. More specifically, he is hoping Nancy may have revealed to Temple a motive for the murder that could save Nancy from execution, and he has the sense that Temple is hiding something and perjured herself in court. While Temple refuses to reveal her secrets that day after Nancy's trial, months later, two days before Nancy's execution, Temple does finally decide she should reveal Nancy's motive.
Temple reveals that Nancy had upbraided Temple for giving into Pete's blackmailing. Nancy had begged Temple not to yield to Pete's desires for her to go off with him and to not slide back into her scandalous past. But in response, Temple argued that she could never escape her past. Therefore, Nancy had smothered Temple's daughter both as punishment and in an effort to bring Temple to her senses.
Hence, when Stevens tells Temple, "The past is never dead," he is underscoring her belief that she will never truly be able to escape her scandalous past. However, Stevens motive in saying so is different from Temple's own belief that she can't escape her past. Temple's belief rests in her self-defeatism; Stevens motive rests in the notion that the stories of the past not only effect the present but can help change the future: Since Nancy's motive rests in Temple's past, a revelation of that past may help save Nancy.
In order to find out what page it is I would need a copy of the book/play. I can tell you that the original quote is actually "The past is never dead. It's not even past." The quote is often paraphrased or misquoted. It would be found in Act 1, scene 3. I hope the original quote will help you find it easier. If you attached a pdf then, I could help you further.