The Further Adventures of Robinson Crusoe by Daniel Defoe Chapter 6 Page 57

and he would never, while his eyes were open, believe that his old master was a heretic, and would be damned; and this might in the end ruin the poor fellow’s principles, and so turn him back again to his first idolatry. However, a sudden thought relieved me in this strait, and it was this: I told him I could not say that I was willing to part with Friday on any account whatever, though a work that to him was of more value than his life ought to be of much more value than the keeping or parting with a servant. On the other hand, I was persuaded that Friday would by no means agree to part with me; and I could not force him to it without his consent, without manifest injustice; because I had promised I would never send him away, and he had promised and engaged that he would never leave me, unless I sent him away.