Agathias, IV, 25, 2-5: But after them Shapur (II) enjoyed his kingdom for by far the longest time, and his reign was as long as his life. For, while his mother was still carrying him, the royal succession summoned the unborn child to the throne. It was not known whether the child would be a boy or a girl. 3. So all the political leaders offered prizes and gifts to the Magi if they could foretell what would come to pass. So they brought out a mare in foal that was very near her time, and told them to prophesy first about this, as they thought the result would be. In this way they reflected that they could know in a few days how their prophecies turned out and thus judge that whatever they prophesied about the woman would turn out in the same way. What they foretold about the mare I cannot say for sure, for I was not told all the details, except that everything came to pass exactly as they had predicted. 4. The others, judging from this that the Magi were accurate at their craft, urged them to reveal what they thought would happen in the case of the woman too. And when they said that the child would be a boy, they waited no longer but held the crown over her stomach and proclaimed the embryo king, designating by this name a creature just formed and shaped just enough, I suppose, to move about and kick a little inside. 5. And so they changed what is naturally uncertain and unknown by their expectation into revealed certainty, yet even so, their hopes did not fail them; they actually achieved their aim, and even more than they had expected. For not long afterwards Shapur was born, at the same time as his kingdom, and he grew up with it and grew old with it, his life lasting for seventy years.
(Cameron, pp. 123-5)