Histories

It is said that Leonidas himself sent them away because he was concerned that they would be killed, but felt it not fitting for himself and the Spartans to desert that post which they had come to defend at the beginning.

I, however, tend to believe that when Leonidas perceived that the allies were dispirited and unwilling to run all risks with him, he told then to depart. For himself, however, it was not good to leave; if he remained, he would leave a name of great fame, and the prosperity of Sparta [22.4417,37.0667] (Perseus) Sparta would not be blotted out.