1 Samuel 17:2

And Saul and the men of Israel were gathered together, and pitched by the valley of Elah, and set the battle in array against the Philistines.

Cross-reference

1 Samuel 17:19 confirms Israel is fighting in the same valley of Elah — immediate narrative continuation.

1 Samuel 21:9 recalls Goliath's sword from the valley of Elah — a later reference to this same battlefield.