1 Samuel 18:3

Then Jonathan and David made an agreement together, because of Jonathan's love for David.

1 Samuel 20:8-17

So, then, be kind to your servant; for you have been united with your servant in an agreement made before the Lord: but if there is any wrongdoing in me, put me to death yourself; why take me to your father?

1 Samuel 20:42

And Jonathan said to David, Go in peace, for we two have taken an oath, in the name of the Lord, saying, The Lord will be between me and you, and between my seed and your seed for ever. Then David went away, and Jonathan went into the town.

1 Samuel 23:18

And the two of them made an agreement before the Lord: and David went on living in Horesh, and Jonathan went back to his house.

2 Samuel 9:1-3

And David said, Is there still anyone of Saul's family living, so that I may be a friend to him, because of Jonathan?

2 Samuel 21:7

But the king did not give up Mephibosheth, the son of Saul's son Jonathan, because of the Lord's oath made between David and Jonathan, the son of Saul.

Treasury of Scripture Knowledge

Summary

Then Jonathan and David made a covenant, because he loved him as his own soul.

Bible References

General references

Genesis 21:32
So they made an agreement at Beer-sheba, and Abimelech and Phicol, the captain of his army, went back to the land of the Philistines.
1 Samuel 23:18
And the two of them made an agreement before the Lord: and David went on living in Horesh, and Jonathan went back to his house.
Proverbs 17:17
A friend is loving at all times, and becomes a brother in times of trouble.

Basic English, produced by Mr C. K. Ogden of the Orthological Institute - public domain