Arrian, Anabasis 6.1
 Since Alexander had ready for him on the banks of the Hydaspes many triakontoroi and hemioliai and many transports for horses and since Alexander had ready for him on the banks of the Hydaspes many triakontoroi and hemioliai and many transports for horses and other vessels useful for the conveyance of an army by river, he determined to sail down the Hydaspes to the Great Sea.  He had already seen crocodiles on the Indus, as on no other river except the Nile, and beans growing on the banks of the Akesines, of the same sort as the land of Egypt produces; and, having heard that the Akesines runs into the Indus, he thought he had found the origin of the Nile.  His idea was that the Nile rose somewhere thereabouts in India, flowed through a great expanse of desert, and there lost the name of Indus, and then, where it began to flow through inhabited country, got the name of Nile from the Ethiopians in those parts and the Egyptians, or that of Aigyptos, which Homer gave in his poem, whence the name of the land, and that it then issued into the inner sea.  In fact when writing to Olympias about the Indian country, Alexander wrote among other things that he thought he had discovered the springs of the Nile, drawing a conclusion about matters of so much importance from very slender indications.  But that, when he had more accurately investigated the geography of the river Indus, he learnt from the inhabitants that the Hydaspes joins its stream to the Akesines and the Akesines to the Indus, and that they resign their names, while the Indus then flows out into the Great Sea by two mouths and has nothing whatever to do with Egypt, and as a result he cancelled the part of the letter to his mother which dealt with the Nile,  and that, with the idea of sailing down the rivers to the great sea he ordered the boats to be made ready for him for this purpose. The crews of his boats were made up from the Phoenicians, Cyprians, Karians and Egyptians who accompanied the expedition.