Passage 9.39.14
γράφω δὲ οὐκ ἀκοὴν ἀλλὰ ἑτέρους τε ἰδὼν καὶ αὐτὸς τῷ Τροφωνίῳ χρησάμενος. τοὺς δὲ ἐς τοῦ Τροφωνίου κατελθόντας, ἀνάγκη σφᾶς, ὁπόσα ἤκουσεν ἕκαστος ἢ εἶδεν, ἀναθεῖναι γεγραμμένα ἐν πίνακι. λείπεται δʼ ἔτι καὶ τοῦ Ἀριστομένους ἐνταῦθα ἡ ἀσπίς· τὰ δὲ ἐς αὐτὴν ὁποῖα ἐγένετο, ἐδήλωσα ἐν τοῖς προτέροις τοῦ λόγου.
I do not write from hearsay, but as one who has seen others and has himself consulted Trophonius. Those who descend to Trophonius are obliged to dedicate on a tablet all that each has heard or seen. Here still remains also the shield of Aristomenes; what happened concerning it, I have already made clear earlier in my account.