While there are various "mentions" of war dogs appearing on the scene at various times, accounts of actual use in battle are fairly scarce. In particular, I am thinking of the dogs "showing up" in: Herodotus, Histories 7.187, where Herodotus mentions the invading Persian army accompanied by "huge packs" of Indian hounds, but never mentions these dogs again.

Nevertheless, I was able to find just a couple of authentic primary source accounts.

First, Aelian (a Greco-Roman historian) mentions a battle in Asia Minor between the inhabitants of Ephesus and Magnesia, ca. 600's BC. He describes how the Magnesians deployed spearmen, each accompanied by a trained hound. When the Ephesian cavalry charged, the Magnesians unleashed the dogs against them, causing "Phoibos" (terror) and "Ataxia" (disorder) among the horsemen. Then the spearmen charged and were able to effectively destroy the Ephesian cavalry. You can find Aelian's account at: http://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A2008.01.0591%3Abook%3D14%3Achapter%3D46. Unfortunately it's only in Greek, but it is quite an interesting read. I would note, however, from a historian's perspective, Aelian lived in the 2nd Century AD - approximately 800 years after the events he describes, so we should question whether his account is entirely accurate. On the other hand, he likely had access to primary sources which are no longer extant.

I was able to find one more primary source account. About 400 years later, in 231 BC the Roman consul Marcus Pomponius Matho invaded Sardinia and when the Sardinians tried to fight him with guerrilla "hit-and-run"tactics, he used "dogs from Italy" to them down in their hiding places. Zonara, Ioannu 'Epitomé historíon' VIII 19 P. I 401. (Greek and latin text only, found at https://archive.org/details/ioannoutouzonara04zonauoft)