Passage 10.8.10
ἤκουσα δὲ καὶ ἄλλο τοιόνδε, τὸ ὕδωρ τῇ Κασταλίᾳ ποταμοῦ δῶρον εἶναι τοῦ Κηφισοῦ. τοῦτο ἐποίησε καὶ Ἀλκαῖος ἐν προοιμίῳ τῷ ἐς Ἀπόλλωνα· βεβαιοῦνται δὲ οὐχ ἥκιστα οἱ Λιλαιεῖς, οἳ ἐς τοῦ Κηφισοῦ τὴν πηγὴν πέμματα ἐπιχώρια καὶ ἄλλα ὁπόσα νομίζουσιν ἀφιᾶσιν ἔν τισιν εἰρημέναις ἡμέραις, καὶ αὖθις ἐν τῇ Κασταλίᾳ φασὶν αὐτὰ ἀναφαίνεσθαι.
I have also heard another account of the following kind, that the waters of Castalia are a gift from the river Cephisus. Alcaeus also said this in his hymn addressed to Apollo; and the people of Lilaea are particularly firm in affirming it. On certain days prescribed by custom, they cast local cakes and other offerings deemed appropriate into the spring of Cephisus, and claim that these same things reappear later in the spring of Castalia.