From Plutarch’s De Gloria Atheniensium (4.347F):
“Corinna warned Pindar, who was still young and prided himself on his eloquence, that he was unpoetic for not telling myths, which are the proper business of poetry, but that he supported his works with unusual words, strange usages, paraphrases, songs, and rhythms, which are just embellishments of the subject matter. So Pindar, taking her words to heart, composed that famous poem, ‘Shall it be Ismenus . . . ?’ When he showed it to her, she laughed and said that one should sow with the hand, not with the whole sack.”
ἡ δὲ Κόριννα τὸν Πίνδαρον, ὄντα νέον ἔτι καὶ τῇ λογιότητι σοβαρῶς χρώμενον, ἐνουθέτησεν ὡς ἄμουσον ὄντα καὶ μὴ ποιοῦντα μύθους, ὃ τῆς ποιητικῆς ἔργον εἶναι συμβέβηκε, γλώττας δὲ καὶ καταχρήσεις καὶ μεταφράσεις καὶ μέλη καὶ ῥυθμοὺς ἡδύσματα τοῖς πράγμασιν ὑποτιθέντα. σφόδρ᾿ οὖν ὁ Πίνδαρος ἐπιστήσας τοῖς λεγομένοις ἐποίησεν ἐκεῖνο τὸ μέλος. δειξαμένου δὲ τῇ Κορίννῃ γελάσασα ἐκείνη τῇ χειρὶ δεῖν ἔφη σπείρειν, ἀλλὰ μὴ ὅλῳ τῷ θυλάκῳ
The line reference is preserved in Psuedo-Lucian’s In Praise of Demosthenes (or the Pindar Loeb v.2 pg. 232)
Shall it be Ismenus, or Melia of the golden spindle,
or Cadmus, or the holy race of the Spartoi,
or Thebe of the dark-blue fillet,
or the all-daring strength of Heracles,
or the wondrous honor of Dionysus,
or the marriage of white-armed Harmonia
that we shall hymn?
Ἰσμηνὸν ἢ χρυσαλάκατον Μελίαν
ἢ Κάδμον ἢ Σπαρτῶν ἱερὸν γένος ἀνδρῶν
ἢ τὰν κυανάμπυκα Θήβαν
ἢ τὸ πάντολμον σθένος Ἡρακλέος
5ἢ τὰν Διωνύσου πολυγαθέα τιμὰν
ἢ γάμον λευκωλένου Ἁρμονίας
ὑμνήσομεν;