Letter 37: Procopius says hearing both brothers together doubles his pleasure.

Well done to your letters, for they know how greatly to lift my mind toward good cheer. What is sweeter than hearing people speak when one has prayed for them to be present, at least by their voices? Fortune should have nodded to this long ago. May it someday happen and come to completion, if you are willing, O gods. Until then, letters must be supplied to me in place of you. One person takes pleasure in being Croesus and possessing his wealth; another in being called the Great King. Another, seeing swallows, decides that he has spring. But enjoying your voice, I felt greater pride than Croesus over those talents or the Great King sitting beneath his plane tree. Instead of swallows, the Muses themselves seemed to sing to me. But I will stop, lest by wanting to show my pleasure too much I appear in these letters to be a sophist, and you laugh with one another and make our familiar joke. Still, the fact that you addressed me together gave me double pleasure, like those who come to Delphi and, after singing a hymn, hold Apollo in their speech while Artemis too shares the song. This gladdened the gods more than if someone had taken each separately and hymned them apart. Being brother and sister, they wished to remain so in songs as well.

Ζαχαρίαι καὶ Φιλίππωι ἀδελφοῖς Εὖγε τῶν ὑμετέρων γραμμάτων, ὡς πρὸς εὐθυμίαν ὅσην ἡμῶν οἶδεν ἐπαίρειν τὴν γνώμην. τί γὰρ ἥδιον ἢ φθεγγομένων ἀκούειν ὅτε παρεῖναί τινας αὑτῷ φθόγγοις προσηύξατο; ὡς ἔδει μὲν καὶ πάλαι τοῦτο τὴν τύχην ἐπινεῦσαι, γένοιτο δ' ἄν ποτε καὶ πρὸς πέρας ἔλθοι βουλομένων ὑμῶν, ὦ θεοί, ἐν ὅσῳ γε μὴν μέλλουσιν ἀνθ' ἑαυτῶν ἡμῖν χορηγεῖσθαι τὰ γράμματα. ἄλλῳ μὲν γὰρ ἐν ἡδονῇ Κροίσῳ τε εἶναι καὶ τἀκείνου κεκτῆσθαι, τῷ δὲ βασιλεὺς ὁ μέγας ἀκούειν· ἄλλος τὰς χελιδόνας ἰδὼν τὸ ἔαρ ἔχειν ὁρίζεται, ἐγὼ δὲ τῆς ὑμετέρας ἀπολαύων φωνῆς μεῖζον ἐφρόνουν ἢ Κροῖσος ἐπὶ τοῖς ταλάντοις ἐκείνοις καὶ βασιλεὺς ὁ μέγας ὑπὸ τῇ πλατάνῳ καθήμενος, καὶ ἀντὶ τῶν χελιδόνων αὐτάς μοι προσᾴδειν ἐδόκουν τὰς Μούσας. ἀλλὰ γὰρ παύσομαι, μὴ τὴν ἡδονὴν ἄγαν ἐμφαίνειν ἐθέλων σοφιστὴς οὕτω που τάχα δόξω τοῖς γράμμασι, καὶ γελῶντες ἀλλήλοις τοῦτο δὴ τὸ σύνηθες ἡμῖν ἐπισκώψητε. πλὴν ὅτι μοι διπλασίαν ἐνεποίει τὴν ἡδονὴν τὸ κοινῇ προσερεῖν ὑμᾶς, ὥσπερ τοῖς εἰς Δελφοὺς ἀφικομένοις, ἐπειδὰν ὕμνον εἰπόντες Ἀπόλλωνά τε σχοῖεν τῷ λόγῳ, καὶ Ἄρτεμις ἅμα μέρος ἦν τῆς ᾠδῆς. τοῦτο δὲ καὶ τοὺς θεοὺς ηὔφραινε μᾶλλον, ἢ εἰ καθ' αὑτόν τις ἀπολαβὼν ἑκάτερον ὕμνησεν. ἀδελφοὶ γὰρ ὄντες καὶ ταῖς ᾠδαῖς τοιοῦτοι μένειν ἠβούλοντο.