One of the most important sources for the history of Greek philosophy is Diogenes Laërtius, whose Lives and Opinions of Eminent Philosophers is often the principal source of information about a given thinker. This is not the case for someone as famous as Pythagoras, but even here, DL (as the common abbreviation goes) is invaluable, since he compiles information from a multitude of sources, and quotes multiple overlapping sources where others might have condensed them into one synthetic account.
One short text of sorts that we owe to this practice is a list of moral injunctions supposedly given by Pythagoras to all of his students (DL 8.22–24). No source is named, but it is evident that the author used the Golden Verses, since line 42 is quoted, and some other contents seem to go back to it as well. But other material is independent of this poem.
It is said that he advised his students:
(1) To say the following whenever they came home: “Where did I overstep? What did I accomplish? What obligation did I not fulfil?” (Golden Verses 42.)
(2) Not to have victims be brought to the gods, but to honor only the the altar unstained by blood.
(3) Not to swear an oath by the gods, because they must strive to show their own person to be worthy of belief.
(4) To honor their elders, in the belief that what precedes in time is more worthy of honor; just as in the cosmos, sunrise comes before sunset, in the course of life (bios), the beginning before the end, and in all life (zôê), origination before destruction.
(5) To honor the gods before daemons, and heroes before humans, but out of all humans, their parents above all.
(6) To behave towards each other in a way that does not turn friends into enemies, but enemies into friends; and to regard nothing as their own [but share everything with their friends?].
(7) To support the law and combat lawlessness.
(8) Never to destroy or injure a wild plant or an animal which does not harm humans.
(9) That having a sense of shame and propriety entails neither to be carried away by laughter nor to wear sullenness on their face.
(10) To flee excess in [eating?] flesh.
(11) To alternate between slackening and exertion when making a journey.
(12) To exercise their memory.
(13) Neither to speak nor to act in anger.
(14) To honor all divination.
(15) To sing to the lyre, and to show due gratitude (kharis) through a hymn of gods and good men.
(16) To abstain from [eating] beans, because they are spiritual (pneumatôdeis) and especially share in the nature of soul (to psykhikon); and besides, not eating them makes the stomach less disturbed. For the same reason, it also makes the sights seen in dreams easy and untroubled.