About the time when Cambyses arrived at Memphis, Apis appeared to the Egyptians. Now Apis is the god whom the Greeks call Epaphus. As soon as he appeared, straightway all the Egyptians arrayed themselves in their gayest garments, and fell to feasting and jollity: which when Cambyses saw, making sure that these rejoicings were on account of his own ill success, he called before him the officers who had charge of Memphis, and demanded of them- “Why, when he was in Memphis before, the Egyptians had done nothing of this kind, but waited until now, when he had returned with the loss of so many of his troops?” The officers made answer, “That one of their gods had appeared to them, a god who at long intervals of time had been accustomed to show himself in Egypt- and that always on his appearance the whole of Egypt feasted and kept jubilee.” When Cambyses heard this, he told them that they lied, and as liars he condemned them all to suffer death.
When they were dead, he called the priests to his presence, and questioning them received the same answer; whereupon he observed, “That he would soon know whether a tame god had really come to dwell in Egypt” — and straightway, without another word, he bade them bring Apis to him. So they went out from his presence to fetch the god. Now this Apis, or Epaphus, is the calf of a cow which is never afterwards able to bear young. The Egyptians say that fire comes down from heaven upon the cow, which thereupon conceives Apis. The calf which is so called has the following marks: — He is black, with a square spot of white upon his forehead, and on his back the figure of an eagle; the hairs in his tail are double, and there is a beetle upon his tongue.
When the priests returned bringing Apis with them, Cambyses, like the harebrained person that he was, drew his dagger, and aimed at the belly of the animal, but missed his mark, and stabbed him in the thigh. Then he laughed, and said thus to the priests: — “Oh! blockheads, and think ye that gods become like this, of flesh and blood, and sensible to steel? A fit god indeed for Egyptians, such an one! But it shall cost you dear that you have made me your laughing-stock.” When he had so spoken, he ordered those whose business it was to scourge the priests, and if they found any of the Egyptians keeping festival to put them to death. Thus was the feast stopped throughout the land of Egypt, and the priests suffered punishment. Apis, wounded in the thigh, lay some time pining in the temple; at last he died of his wound, and the priests buried him secretly without the knowledge of Cambyses.
And now Cambyses, who even before had not been quite in his right mind, was forthwith, as the Egyptians say, smitten with madness for this crime.
Cambyses no sooner heard the name of Smerdis than he was struck with the truth of Prexaspes’ words, and the fulfilment of his own dream- the dream, I mean, which he had in former days, when one appeared to him in his sleep and told him that Smerdis sate upon the royal throne, and with his head touched the heavens. So when he saw that he had needlessly slain his brother Smerdis, he wept and bewailed his loss: after which, smarting with vexation as he thought of all his ill luck, he sprang hastily upon his steed, meaning to march his army with all haste to Susa against the Magus. As he made his spring, the button of his sword-sheath fell off, and the bared point entered his thigh, wounding him exactly where he had himself once wounded the Egyptian god Apis. Then Cambyses, feeling that he had got his death-wound, inquired the name of the place where he was, and was answered, “Agbatana.” Now before this it had been told him by the oracle at Buto that he should end his days at Agbatana. He, however, had understood the Median Agbatana, where all his treasures were, and had thought that he should die there in a good old age; but the oracle meant Agbatana in Syria. So when Cambyses heard the name of the place, the double shock that he had received, from the revolt of the Magus and from his wound, brought him back to his senses. And he understood now the true meaning of the oracle, and said, “Here then Cambyses, son of Cyrus, is doomed to die.”
– Herodotos, The Histories 3.28ff