What happened between David and Goliath is found in Genesis 20 and 21

Here is the text in the World English Bible (WEB) translation. Its in the public domain so feel free to copy and spread everywhere.

Genesis 20

Abraham and Abimelech

¹ Abraham traveled from there toward the land of the South, and lived between Kadesh and Shur. He lived as a foreigner in Gerar. ² Abraham said about Sarah his wife, “She is my sister.” Abimelech king of Gerar sent, and took Sarah. ³ But God came to Abimelech in a dream of the night, and said to him, “Behold, you are a dead man, because of the woman whom you have taken; for she is a man’s wife.”
⁴ Now Abimelech had not come near her. He said, “Lord, will you kill even a righteous nation? ⁵ Didn’t he tell me, ‘She is my sister’? She, even she herself, said, ‘He is my brother.’ I have done this in the integrity of my heart and the innocence of my hands.”
⁶ God said to him in the dream, “Yes, I know that in the integrity of your heart you have done this, and I also withheld you from sinning against me. Therefore I didn’t allow you to touch her. ⁷ Now therefore, restore the man’s wife. For he is a prophet, and he will pray for you, and you will live. If you don’t restore her, know for sure that you will die, you, and all who are yours.”
⁸ Abimelech rose early in the morning, and called all his servants, and told all these things in their ear. The men were very scared. ⁹ Then Abimelech called Abraham, and said to him, “What have you done to us? How have I sinned against you, that you have brought on me and on my kingdom a great sin? You have done deeds to me that ought not to be done!” ¹⁰ Abimelech said to Abraham, “What did you see, that you have done this thing?”
¹¹ Abraham said, “Because I thought, ‘Surely the fear of God is not in this place. They will kill me for my wife’s sake.’ ¹² Besides, she is indeed my sister, the daughter of my father, but not the daughter of my mother; and she became my wife. ¹³ When God caused me to wander from my father’s house, I said to her, ‘This is your kindness which you shall show to me. Everywhere that we go, say of me, “He is my brother.” ’ ”
¹⁴ Abimelech took sheep and cattle, male servants and female servants, and gave them to Abraham, and restored Sarah, his wife, to him. ¹⁵ Abimelech said, “Behold, my land is before you. Dwell where it pleases you.” ¹⁶ To Sarah he said, “Behold, I have given your brother a thousand pieces of silver. Behold, it is for you a covering of the eyes to all that are with you. In front of all you are vindicated.”
¹⁷ Abraham prayed to God. So God healed Abimelech, his wife, and his female servants, and they bore children. ¹⁸ For Yahweh had closed up tight all the wombs of the house of Abimelech, because of Sarah, Abraham’s wife.

Genesis 21

Isaac’s birth

¹ Yahweh visited Sarah as he had said, and Yahweh did to Sarah as he had spoken. ² Sarah conceived, and bore Abraham a son in his old age, at the set time of which God had spoken to him. ³ Abraham called his son who was born to him, whom Sarah bore to him, Isaac.* ⁴ Abraham circumcised his son, Isaac, when he was eight days old, as God had commanded him. ⁵ Abraham was one hundred years old when his son, Isaac, was born to him. ⁶ Sarah said, “God has made me laugh. Everyone who hears will laugh with me.” ⁷ She said, “Who would have said to Abraham that Sarah would nurse children? For I have borne him a son in his old age.”
⁸ The child grew and was weaned. Abraham made a great feast on the day that Isaac was weaned.

Hagar in the dessert

⁹ Sarah saw the son of Hagar the Egyptian, whom she had borne to Abraham, mocking. ¹⁰ Therefore she said to Abraham, “Cast out this servant and her son! For the son of this servant will not be heir with my son, Isaac.”
¹¹ The thing was very grievous in Abraham’s sight on account of his son. ¹² God said to Abraham, “Don’t let it be grievous in your sight because of the boy, and because of your servant. In all that Sarah says to you, listen to her voice. For your offspring will be named through Isaac. ¹³ I will also make a nation of the son of the servant, because he is your child.” ¹⁴ Abraham rose up early in the morning, and took bread and a container of water, and gave it to Hagar, putting it on her shoulder; and gave her the child, and sent her away. She departed, and wandered in the wilderness of Beersheba. ¹⁵ The water in the container was spent, and she put the child under one of the shrubs. ¹⁶ She went and sat down opposite him, a good way off, about a bow shot away. For she said, “Don’t let me see the death of the child.” She sat opposite him, and lifted up her voice, and wept. ¹⁷ God heard the voice of the boy.
The angel of God called to Hagar out of the sky, and said to her, “What troubles you, Hagar? Don’t be afraid. For God has heard the voice of the boy where he is. ¹⁸ Get up, lift up the boy, and hold him with your hand. For I will make him a great nation.”
¹⁹ God opened her eyes, and she saw a well of water. She went, filled the container with water, and gave the boy a drink.
²⁰ God was with the boy, and he grew. He lived in the wilderness, and as he grew up, he became an archer. ²¹ He lived in the wilderness of Paran. His mother got a wife for him out of the land of Egypt.

covenant with Abimelech

²² At that time, Abimelech and Phicol the captain of his army spoke to Abraham, saying, “God is with you in all that you do. ²³ Now, therefore, swear to me here by God that you will not deal falsely with me, nor with my son, nor with my son’s son. But according to the kindness that I have done to you, you shall do to me, and to the land in which you have lived as a foreigner.”
²⁴ Abraham said, “I will swear.” ²⁵ Abraham complained to Abimelech because of a water well, which Abimelech’s servants had violently taken away. ²⁶ Abimelech said, “I don’t know who has done this thing. You didn’t tell me, and I didn’t hear of it until today.”
²⁷ Abraham took sheep and cattle, and gave them to Abimelech. Those two made a covenant. ²⁸ Abraham set seven ewe lambs of the flock by themselves. ²⁹ Abimelech said to Abraham, “What do these seven ewe lambs, which you have set by themselves, mean?”
³⁰ He said, “You shall take these seven ewe lambs from my hand, that it may be a witness to me, that I have dug this well.” ³¹ Therefore he called that place Beersheba,† because they both swore an oath there. ³² So they made a covenant at Beersheba. Abimelech rose up with Phicol, the captain of his army, and they returned into the land of the Philistines. ³³ Abraham planted a tamarisk tree in Beersheba, and there he called on the name of Yahweh, the Everlasting God. ³⁴ Abraham lived as a foreigner in the land of the Philistines many days.