It's even older than aired Trek, technically. William James wrote it down in a book published in 1897, attributing it to an acquaintance. There are other examples of real-world origins for lines spoken by Trek characters, (Soran's "Time is the fire in which we burn" in Generations, for one) but this one does sound particularly like something you could expect to hear Spock say, whether he actually did so on-screen or not.I had the same problem with the quote I attributed to Spock "A difference that makes no difference is no difference". On another thread I was told it only appeared in some Trek novel. However, when you google it there are numerous references to this quote Spock, yet nobody references the episode where Spock actually says this quote.
It is from SPOCK MUST DIE! It is so old that people think it must be from aired trek, but it is not.