I’ve made the point repeatedly that we can never know for sure what the Buddha actually said. All we have to go on are scriptures that were at first passed on orally for two centuries or more, and then were committed to writing. If a quote attributed to the Buddha isn’t in the scriptures, or can be reliably attributed to someone else, then we can be fairly confident in saying that it’s fake. But we can never say with 100% certainly that any given quote from the scriptures is genuine.
It’s a convention that what’s in the scriptures is Buddha-vacana — the word of the Buddha — unless there’s very good reason to believe otherwise. And there is sometimes clear evidence that the scriptures have been tampered with.
Buddha-vacana.org has an interesting example of this, in what happens to be one of my favorite suttas, The Great Forty, or Mahācattārīsaka Sutta. If you’re into studying the suttas, then this apparently anonymous article is a must-read. Here’s the conclusion:
It has been demonstrated in this analysis that in this sutta:
1) there are some teachings that we find in other suttas as well.
2) there are peculiar teachings not found anywhere else that look quite authentic, which tends to prove that there would be an authentic version of this sutta.
3) there are distinctions made in the teachings of the Buddha, which are apparently based on an opinion expressed in the Khuddaka Nikāya and according to which there is an ‘inferior’ portion of the teaching siding with merit etc. and a superior ‘noble’ one connected with insight etc.
4) the word ‘sāsava’ is used here in a sense which is consistent with late literature, but that is in direct contradiction with otherwise well-known teachings of the four Nikāyas, which proves that the falsification of this sutta has taken place late enough for this semantic drift to have happened.
5) we find very rare words and expressions found only in the Khuddaka Nikāya or the Abhidhamma, and not anywhere else in the four Nikāyas.
6) alternate definitions of the factor of the path are given, which are doubtlessly taken from the Abhidhamma, since outside this sutta they do not appear anywhere else than there.
7) there is an underlying contempt of the ancient teachings and the author seeks to promote teachings found in the Khuddaka Nikāya and Abhidhamma.
This is more than enough to prove that this sutta, though it seems to contain original and authentic material, has been largely falsified.
This study has also shown that even in what is to be considered as the most ancient strata of buddhist scriptures, there are counterfeit teachings aiming at belittling the original message of the Buddha in order to promote newer terminologies and theories, that are presented as being of higher value, but that actually contradict the ancient teachings.
The analysis shows quite convincingly that later teachings, the Abhidhamma, have been incorporated into this sutta and in effect put into the mouth of the Buddha. As well as the fake parts, the sutta actually contains some apparently genuine and very interesting teachings on the eightfold path. Fortunately it was largely those parts of the sutta that I had been most drawn to and that had led to it being one of my favorites.
I did recently see someone claiming, in all seriousness, that the Abhidhamma was taught by the Buddha, but that’s a completely untenable position, held only by those of “great faith” and little inclination to accept evidence.
I do suggest taking a look at the article.