Passage 4.21.8
οὗτος δὲ καὶ στρατήγημα ἐξεῦρε τοιόνδε. ἀριθμῷ καὶ πολὺ οἱ Λακεδαιμόνιοι περιῆσαν· ἅτε δὲ οὐκ ἐν εὐρυχωρίᾳ σφίσιν οὐδὲ κατὰ σύνταγμα ἐγγινομένης τῆς μάχης, ἄλλων δὲ ἐν ἄλλῳ τῆς πόλεως ποιουμένων τὸν ἀγῶνα, ἀχρείους ἀπὸ ἑκάστης τάξεως συνέβαινεν εἶναι τοὺς τελευταίους. τούτους ἐκέλευεν ἀποχωρήσαντας ἐς τὸ στρατόπεδον σιτίων μεταλαβεῖν καὶ ὕπνου καὶ αὖθις πρὸ ἑσπέρας ἥκειν τοῖς ὑπομενοῦσιν αὐτῶν διαδεξομένους τὸν πόνον.
He also devised the following stratagem. The Spartans greatly outnumbered his force; however, since the battle took place neither in open ground nor in regular formation, but instead was fought with different groups engaging separately in various parts of the city, it happened that the rearmost ranks of each unit were inactive. He ordered these men to withdraw to the camp, partake of food and rest, and then return again before evening, relieving in turn their comrades who had remained to endure the battle.