"A most severe decree against all who directly or indirectly practised any arts of magic, or who were in possession of any books of a magical character, had been passed by Valentinian and Valens. This decree was being enforced at this time with great rigour and cruelty at Antioch. Those charged— often times on the most frivolous grounds—with any complicity with such practices were liable to exile, torture, and even death. Soldiers were employed in carefully searching for suspected persons, and dragging them before the legal tribunals. Informers, too, abounded on every side. And not only soldiers and informers, but judges also were eager to court imperial favour by carrying out the decree with rigour and severity. No age or sex escaped. The prisons, not only in the capital, but also at Antioch, were filled with persons of all ranks and professions charged with offenses connected with magical rites, or with having in their possession books either actually bearing on magic or supposed to bear upon it. Men, in their terror, destroyed their whole libraries in order to avoid all suspicion.
When such was the state of feeling at Antioch in connection with magic, it happened that one day Chrysostom and a friend were walking on the outskirts of the city, in the gardens by the banks of the Orontes, towards the chapel of the martyr Babylas. As they were proceeding along the margin of the river, they saw some leaves of a book floating down the stream. In emulous sport they tried to catch the leaves as they passed along upon the surface of the water. They succeeded in securing some of them, when, to their consternation, they discovered that they were filled with magical signs and symbols. At this critical moment a soldier was observed approaching them. What could they do with those fatal leaves ? Should they hide them about their persons, or cast them back again into the river? If they hid them, the soldier might prosecute a search, and discovery might lead to the most fatal consequences ; if they threw them into the river again, the soldier might see the act, recover the leaves, and fasten a charge upon them for having had such a book in their possession. They hesitate in alarm as to their course of conduct, rapidly weighing and balancing in their mind the probable effect of either line of action. At last they determine to commit those perilous leaves once more to the river. Fortunately for them their conduct was unobserved by the soldier, who passed on in ignorance both of their terror and of what they had done. They thus escaped; but the fears of Chrysostom were greatly excited by the event, and he could not refrain from attributing his escape to the merciful providence of God".
The above is a rather embellished version in the Victorian taste. The more basic bones of the story, as related in Florent Heintz's essay on circus curse tablets ,is to be found in Patrologia Graeca Vol 60 pg 275.
The whole little incident is interesting as it gives the rather odious Chrysostom an almost human aspect, well at least as a child/teen.
It is also interesting to note they were wandering along the Orontes bank near the shrine of Saint Babylas that was identified as being on the right bank of the river, opposite the imperial palace.
The timing is also interesting for it is around the time of the "witch hunt" (quite literally) that was let loose with particular ferocity in Antioch by Valens in his fear that magic was being used to divine when his reign would come to an end. These events are well described in the essay "Les procès d’Antioche de 371/2 (Ammien Marcellin 29.1-2) : un cas de persécution religieuse?" by Éric Fournier.