1 Samuel 18:3 records the first covenant between Jonathan and David, which is renewed here in 23:18.

1 Samuel 20:12-17 details the earlier covenant where Jonathan and David pledge loyalty, renewed in 23:18.

1 Samuel 20:42 concludes that covenant with a blessing, and 23:18 is a later renewal of that same bond.

1 Samuel 20:8 has David appeal to the covenant, which is the same bond renewed in 23:18.

2 Samuel 9:1 shows David fulfilling the covenant by seeking to show kindness to Jonathan's house.

2 Samuel 21:7 explicitly cites the oath between David and Jonathan as the reason Mephibosheth was spared.