Letter 21: Procopius recommends Diodorus to Sosianus as a friendship gift.

If a man loves money, nothing would please him more than talking about it and hearing others talk about it. If you brought him gold as well, you would hold the first place in his esteem. If a man's whole life is in arms, give him a fine shield and he is proud at once; carrying the possession here and there, he is filled all the more with Ares. But how could anyone gratify a good man except by letting him see men like himself? Since I know that you are such a man, both by character and by desire, it seemed wrong for me to let you remain ignorant of Diodorus the scholasticus. So I bring him and give him to you, and you to him. I think I will oblige you both if you come to know one another. Each of you will certainly praise me for knowing what sort of introductions to make among friends.

Σοσιανῶι Εἴ τις χρημάτων ἐστὶν ἐραστής, οὐδὲν ἂν ἡδέως ἢ ταῦτα λέγοι καὶ λεγόντων ἄλλων ἀκούσειεν. εἰ δὲ καὶ χρυσὸν ἄγων παράσχοις, ἔχεις τὰ πρῶτα τῆς παρ' ἐκείνῳ τιμῆς. ὅτῳ δὲ ἐν ὅπλοις τὰ πράγματα, καλὴν οὗτος ἀσπίδα λαβὼν ἐφρόνησέ τε μέγα καὶ τῇδε κἀκεῖσε περιφέρων τὸ κτῆμα πληροῦται μᾶλλον τοῦ Ἄρεος. ἀνδρὶ δὲ ἀγαθῷ τί πράττων ἄν τις χαρίσαιτο ἢ παραπλησίους ἄνδρας παρέχων ἰδεῖν; ὅθεν σε τοιοῦτον εἰδὼς καὶ γεγονότα καὶ εἶναι βουλόμενον, τὸν σχολαστικὸν Διόδωρον ἀγνοεῖν οὔ μοι πρέπον ἐφαίνετο, ἀλλ' ἄγω καὶ δίδωμι σοὶ μὲν ἐκεῖνον, ἐκείνῳ δὲ σέ, ἀμφοτέροις ὑμῖν χαριεῖσθαι νομίζων, εἰ ἀλλήλων ἐν πείρᾳ γενήσεσθε. ἐπαινέσει δέ με πάντως ἑκάτερος οἷα τοῖς φίλοις προξενεῖν ἠπιστάμην.