Iamblichus' Life of Pythagoras

...had become weaker, did not resist the sailors' assistance in descending, and immediately upon their departure, ate enough fruit to restore his strength. From there, he arrived safely at the neighboring lands, consistently preserving the same tranquility and modest behavior.

CHAP. IV.

But here, while he frequented all the Egyptian temples with great diligence and thorough investigation, he was admired and loved by the priests and prophets with whom he associated. Having learned every detail with great care, he did not neglect to hear of any significant contemporary event, any man famous for his wisdom, or any mystery, however it might be performed. He did not omit any place where he thought something excellent might be found. On this account, he visited all the priests, by whom he was supplied with the wisdom each possessed. He spent twenty-two years in Egypt, in the adyta (the innermost, most sacred parts of the temples), studying astronomy and geometry, and was initiated—not in a superficial or casual manner—into all the mysteries of the Gods. Eventually, he was taken captive by the soldiers of CambysesKing of Persia, who conquered Egypt in 525 BCE. and brought to Babylon. There, he gladly associated with the Magi, was instructed by them in their venerable knowledge, and learned from them the most perfect worship of the Gods. Through their assistance, he reached the summit of arithmetic, music, and other disciplines; after associating with them for twelve years, he returned to Samos at about fifty-six years of age.