It was fought between at least one Jedi capital ship and a Krath force that came from the Malastare system.
From what is known, the Jedi destroyed most or all of their opponents, but their ships sustained heavy damage and crash-landed on the only world in that star system, Haruun Kal.
The Krath forces moved on to the Sullust system.
Their descendants were undoubtedly the Force-sensitive "Korunnai" people, to whom Jedi Master Mace Windu belonged.
The Battle of Al'Har was mentioned in Shatterpoint. In The Essential Atlas, that a battle was fought in the Haruun Kal system was stipulated on the galactic map showing the battles of the Great Sith War.
- The Essential Atlas