Quintus Curtius Rufus, History of Alexander 8.14.7

8.14.7

Anceps id malum utrisque erat. Nam et Macedonum pedites primo impetu obterebantur, et per lubrica atque invia inmissi currus excutiebant eos, a quibus regebantur.

The Scythians and Dahae first of all attacked the Indians, and then the king launched Perdiccas with his horse upon their right wing. The fighting had now become hot everywhere, when the drivers of the chariots rode at full speed into the midst of the battle, thinking they could thus most effectively succour their friends. It would be hard to say which side suffered most from this charge, for the Macedonian foot-soldiers, who were exposed to the first shock of the onset, were trampled down, while the charioteers were hurled from their seats, when the chariots in rushing into action jolted over broken and slippery ground. Some again of the horses took fright and precipitated the carriages not only into the sloughs and pools of water, but even into the river itself.