Passage 3.6.9
Κλεομένει δὲ τῷ Λεωνίδους τά τε ἄλλα ὁποῖα ἐς τόλμαν ἐτόλμησαν ὁμοῦ καὶ ἀνδρείαν ὑπῆρξε καὶ ὡς ἐπαύσαντο ἐξ ἐκείνου Σπαρτιᾶται βασιλευόμενοι, πρότερον ἔτι ἐδήλωσέ μοι τὰ ἐς τὸν Σικυώνιον Ἄρατον· προσεπελάβετο δὲ ὁ λόγος μοι καὶ τρόπον ὅντινα ἐν Αἰγύπτῳ Κλεομένης ἐτελεύτησεν.
The daring and courage with which Cleomenes son of Leonidas performed his other exploits, and how after him the Spartans ceased to be ruled by kings, I have already previously explained through my account of Aratus the Sicyonian; my narrative then included also the manner of Cleomenes' death in Egypt.