History of the Peloponnesian War
Thucydides
Thucydides, Vol. 1-4. Smith, Charles Foster, translator. London and Cambridge, MA: Heinemann and Harvard University Press, 1919-1923.
even as it was, he was confronted on his march, when he reached the river Enipeus, by other Thessalians belonging to the opposite party. These tried to stop him, warning him that he was doing wrong in proceeding without the consent of the whole people.
But his conductors reassured them, saying that, it they were unwilling, they would not conduct him further, and that they were merely playing the part of hosts in escorting an unexpected visitor. Brasidas himself explained that he came as a friend to Thessaly and its inhabitants and was bearing arms against the Athenians, who were enemies, and not against them; moreover, he was not aware of any such hostility between the Thessalians and the Lacedaemonians as to debar them from access to each other's territory, but if in this instance they were unwilling, he would go no further, nor indeed could he do so;
he hoped, however, that they would not bar his progress. On hearing this the Thessalians departed; but Brasidas, taking the advice of his escort, before a larger force could be collected to hinder him, set out at full speed and without making any halt. In fact, he finished the journey to Pharsalus on the same day on which he had set out from Meliteia, and encamped on the river Apidanus;