Shadrach, Meshach, and Abednego were the Babylonian names of three Jews from the Kingdom of Judah that were living in the Court of Nebuchadnezzar II on a work study program to learn Babylonian ways and culture (In reality, the were basically prisoners, but well cared for.)

Daniel and these three men were expected to eat the special health promoting royal food, which was apparently great stuff, but Daniel was worried that since he had no way to know how or with what it was prepared (It could have been, and probably was ceremonially unclean), asked permission for the four of them to eat only vegetables.

Nebuchadnezzar allowed them to do so on a ten day trial, and if after ten days they looked as healthy as the rest of the young men, they would be allowed to continue with their vegetarian diet.

After ten days they looked better nourished and healthier than all the rest of the young men, so they were allowed to continue.

It is implied in the story that eating only vegetables was not considered a healthy or optimum diet at the time, and it was a surprise to the king that the men looked so healthy after eating what would have been considered a poor diet.

Edit: Fixed a screw up.

605-562 BC. Daniel Chapter 1.

hi! you may be interested in these threads on vegetarianism in the ancient world

• Were all the ancient Egyptians mostly vegetarian, or just the higher class and priests?

• Who is the first vegetarian considered a historical figure?

• When, where, and why did vegetarianism begin as a conscious movement?

• Are there any Ancient recordings of important members of society being Vegetarian, Vegan or pro Animal rights?

• Has there been a successful, strictly vegetarian culture?

As a general note, the earliest things relevant to this issue – to a non-violent coexistence of humans and animals – might be located in those cosmogonies (Greek, etc.) that imagined a more utopian “Golden Age” in the mythic past, but from which we have fallen. It’s common in this regard to cite Hesiod’s Works and Days, here; and the comments in Walters and Portmess (2001:14) are typical (at least typical of non-specialty studies):

The obvious suggestion in Hesiod's description of the five ages is that the slaughter of animals for food only began in the post-golden age period, and that there is a common and reprehensible link between the taste for animal blood, the urge to slay humans, and the perversion of original innocence. The clear implication is that a life of nonviolence . . . is pleasing to the gods as well as ultimately fulfilling for humans, and that the shattering of the prohibition against bloodshed led to the primordial fall.

Yet this is not obvious at all to me (and surely other commentators). I imagine many people have seized on line 146 here where it's said, of those in the Bronze Age, οὐδέ τι σῖτον ἤσθιον (that they did not eat grain), which I suppose is interpreted to mean that their diet has now switched to a carnivorous one. (In addition to this, I suspect the general context of agricultural fecundity is also argued here: καρπὸν δ᾽ ἔφερε ζείδωρος ἄρουρα αὐτομάτη πολλόν τε καὶ ἄφθονον).

But overlooked are those critical comments about those in the Silver Age, ἤθελον οὐδ᾽ ἔρδειν μακάρων ἱεροῖς ἐπὶ βωμοῖς – that they refuse to make sacrifice to the gods. (Also, there's the mention of those in the Golden Age being ἀφνειοὶ μήλοισι, “rich in flocks,” in line 120).

Speaking of other cosmogonies, it's interesting that, in the first chapter of the book of Genesis, only plants are explicitly assigned for food, to both humans and non-human animals (Gen 1:29-30). Later commentators would develop this notion more; though it probably shouldn't pushed that far -- oh and note that, just a few chapters later, Abel's animal sacrifice would be looked up with favor by God, whereas Cain's grain offering would not. (On a final note here, it's interesting how the early strata of the book of Enoch seem to have some sort of cross-pollination of the aforementioned Greek and Jewish traditions here.)

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Turning to the East, the issue of early Indian vegetarianism is hard to parse: both in its development and function (which is often wrapped up with a more general ahiṃsā [non-violence]), etc. Heesterman lauds Alsdorf (whose Beiträge zur Geschichte von Vegetarismus und Rinderverehrung in Indien was an important study of Indian vegetarianism) for emphasizing that ahiṃsā was "not a monopoly of Jains and Buddhists but . . . a common . . . movement in which Brahmanism, Buddhism and Jainism equally shared" (“Non-violence and Sacrifice”). But reflected in some of the texts of these traditions is a "paradoxical juxtaposition of both normative meat-eating and its equally normative rejection" -- which obviously complicates things.

Considering lack of space here (and a lack of a totally intimate familiar with the material here), I'll just settle with saying that the earliest clear formulations of ethical/ritual vegetarianism in Indian tradition can probably be located somewhere close to the middle of the first millennium BCE. For clear formulations in texts themselves, see Manusmṛti 5.48. (Also, there's been a lot of debate about the presence or lack thereof of vegetarianism in the Jain text Ācārāṅga Sūtra.)

For more in-depth info, you're definitely going to want to look into Alsdorf's The History of Vegetarianism and Cow-Veneration in India (and maybe Chapple's Nonviolence to Animals, Earth, and Self in Asian Traditions).

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In terms of Greek tradition, Pythagoreanism is the name of the game here. The situation is actually remarkably similar to the Indian one in several ways (which I could maybe elaborate on more if anyone's interested); and before anything else, some of the ambiguities (and points of clarity) should be pointed out.

We have good evidence that the Pythagorean Empedocles had a very developed notion of metempsychosis -- with Diogenes Laertius even noting that he thought he "was a bush, bird, and fish in previous lives." In this regard he makes pretty unequivocal intimations towards vegetarianism. However, in reference to this -- and to Pythagoras himself -- Burkert notes that

The self-evident corollary of the doctrine of metempsychosis would have to be complete vegetarianism. Empedocles drew this conclusion, and according to Eudoxus, Pythagoras was not only a vegetarian but avoided any association with butchers and hunters.

However, Aristotle's pupil Aristoxenus

asserted that [Pythagoras] only avoided eating plow oxen and rams, but was especially fond of the meat of tender young kids, sucking pigs, and cockerels. Hints of Athenian ways here are intended to lessen the absurdity of Pythagoreanism, for the benefit of the reading public. There are other remarkably persistent traditions that seem to know nothing of Pythagoras as vegetarian. The famous sacrifice of an ox to celebrate a geometrical discovery is attested by a (probably) fourth-century source, and the tradition is hardly later that it was precisely Pythagoras who introduced the meat diet for athletes.

Burkert continues by noting how later commentators tried to deal with these conflicting opinions:

Nicomachus smoothed out the contradictions of the evidence by use of the reports about degrees of membership within the society: the θεωρητικοί practiced complete abstention, whereas the πολιτικοὶ ἢ ἀκουσματικοί ate meat, though "seldom." But the very Pythagoreans whom we must suppose to be "acusmatics," the "Pythagorists," Diodorus of Aspendus, and the Cynic-influenced Onesicritus, emphasize the radical formulation ἐμψύχων ἀπέχεσθαι, while Aristoxenus seems to be thinking rather of "theoretical" Pythagoreans, who still like meat.

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...okay, that's enough for now. Sorry if I get super technical in places. (I'm certainly willing to clarify if anyone needs it.)