From the Greek sources :
"The whole region from Phrygia to the Indus was subject to Seleucus. He crossed the Indus and waged war with Sandrocottus [Maurya],
king of the Indians, who dwelt on the banks of that stream, until they came to an understanding with each other and contracted a marriage relationship."
The geographical position of the tribes is as follows: along the Indus are the Paropamisadae, above whom lies the Paropamisus mountain: then, towards the south, the Arachoti: then next, towards the south, the Gedroseni, with the other tribes that occupy the seaboard; and the Indus lies, latitudinally, alongside all these places; and of these places, in part,
some that lie along the Indus are held by Indians, although they formerly belonged to the Persians. Alexander [III 'the Great' of Macedon] took these away from the Arians and established settlements of his own, but Seleucus Nicator gave them to Sandrocottus [Chandragupta], upon terms of intermarriage and of receiving in exchange five hundred elephants.
Strabo 15.2.9"
"Most geographers, in fact, do not look upon India as bounded by the river Indus, but add to it the four satrapies of the Gedrose, the Arachotë, the Aria, and the Paropamisadë, the River Cophes thus forming the extreme boundary of India. According to other writers, however, all these territories, are reckoned as belonging to the country of the Aria. Pliny, Natural History VI, 23"
Pliny the Elder, The Natural History (eds. John Bostock, M.D., F.R.S., H.T. Riley, Esq., B.A.)
Ashoka only conquered kalinga , rest of the territories were already under the Mauryas . Chandragupta Maurya had acquired lands upto eastern persia by defeating Seleucus Nicator.