The title is as close as I could get it. There's a Russian idiom, meaning that you will do everything for a friend. Actually, not only for a friend. It may be for love, or anything else. If I were to translate it literally, I'd say:
What can't be done for a friend (or for love, you name it)?
Do note, that the question above is rhetorical. Is there a similar idiom in English? What would be the closest translation?
UPD Let me add some more context. Your friend asks you something. You find it weird. You wouldn't do such a thing if not for him. But you do it, saying the phrase being discussed.
UPD Let me add some more context (2nd try). Your friend and you have different idea of what is right to do in some particular situation. You decide to do what he suggested. But make it clear, that if it were you alone, you'd do it your way.