What does Faber say to Montag about the night's event?

I assume you are asking about when Montag kills Beatty and then goes on the run. Faber tells Montag that he may have been foolish in his actions, particularly killing Beatty, but at least Montag was foolish about the right thing.  He also tells Montag where to go and how to get there.  Faber knows there are book people out there and while he doesn't tell Montag to head to them by name, he tells him to go to the river and what to do afterward.  Finally he tells Montag that he is willing to stay and suffer the consequences of actions of having helped Montag, but also he is willing to suffer the consequences of his actions of having done nothing to stop the society from becoming what it has become.  Faber indicated earlier to Montag, that he saw the signs, he saw the way things were headed and he did nothing.  He calls himself a coward for having simply sat back and let it all happen while silently hating it. Before Montag leaves, Faber says, "I deserve everything.  Run, for God's sake."  Faber's purpose in the story becomes clear at this point.  He is representative of those people who see bad things happening, who can detect the bad or negative trends, and do nothing to stop them.