The Deeper Symbolism of Freemasonry from The Meaning of Masonry by Walter Leslie Wilmshurst.

“Our own teaching, for instance, recognizes Pythagoras as having undergone numerous initiations in different parts of the world, and as having attained great eminence in the science. Now it is perfectly certain that Pythagoras was not a Mason at all in our present sense of the word but it is also perfectly certain that Pythagoras was a very highly advanced master in the knowledge of the secret schools of the Mysteries, of whose doctrine some small portion is enshrined for us in our Masonic system.” [via]