rom the Commentary to the Mahāparinibbānasuttaṁ (DN 16)
But in the list [of four things] beginning with sutta, sutta means
the three baskets [Suttanta, Vinaya, Abhidhamma] which the three
Accordance with sutta' means legitimate by being in accord [with what is explicitly legitimate].
The word of a teacher’ means the Commentary.
One's own opinion' means one's own illumination through grasping an analogy or one's consequent understanding. Of these, sutta should not be rejected, for he who rejects that rejects the Buddha himself. If what is legitimate by being in accord agrees with the sutta, it should be accepted, but otherwise not. If the word of a teacher agrees with the sutta, it should be accepted, but otherwise not. One's own opinion is weakest of all, but if it agrees with the sutta, it should be accepted, but otherwise not.
The three Councils’ are the one of five hundred monks, the one of
seven hundred, the one of a thousand. Only a sutta transmitted
through them is authoritative; any other is a contemptible sutta, not
to be accepted. Even though words and syllables appear in the latter,
they should be known `as ones which do not appear in the Sutta, are
not found in the Vinaya.