The Ammonihah prisoners were Nephite inhabitants of the city of Ammonihah and its borders carried captive into the wilderness when a Lamanite army attacked in the eleventh year of the reign of the judges. The Lamanites came in on the wilderness side, slew the people, and destroyed the city; before the Nephites could raise an army to drive them out, they had killed those in Ammonihah and some around the borders of Noah and taken others captive (Alma 16:2-3). The city had earlier rejected and cast out the prophet Alma and his companion Amulek (Alma 8-15).
Zoram, the chief captain over the Nephite armies, with his two sons Lehi and Aha, went to Alma — who was high priest over the church and had the spirit of prophecy — to learn where the Lord would have them go after their captured brethren (Alma 16:5). Alma inquired of the Lord and told them the Lamanites would cross the river Sidon in the south wilderness, beyond the borders of Manti, where they would meet them on the east of the river and recover the captives; Zoram and his sons marched there with their armies (Alma 16:6-7).
They came upon the Lamanite army, scattered and drove it into the wilderness, and recovered all the captives without the loss of a single soul, returning them to their own lands (Alma 16:8).