Arrian was able to use sources which are now lost, such as the contemporary works by Callisthenes (the nephew of Alexander's tutor Aristotle), Onesicritus, Nearchus, and Aristobulus, and the slightly later work of Cleitarchus.
He mentions 14 authors, some of whom believed the story (so Onesicritus, Cleitarchus), while others took it to be only fiction (so Aristobulus of Cassandreia, Chares of Mytilene, Ptolemy I of Egypt, Duris of Samos).