1 Samuel 20:16
So Jonathan made a covenant with the house of David, saying, Let the LORD even require it at the hand of David’s enemies. So Jonathan made a covenant with the house of David, saying, Let the LORD even require it at the hand of David’s enemies.
The covenant united Jonathan and David as brethren, growing from Jonathan's soul being knit to David's soul and loving him as his own soul after David slew Goliath, when Saul kept David with him and would not let him return to his father's house. Jonathan expressed the covenant by stripping himself of the robe upon him and giving it to David, with his garments, even his sword and his bow and his girdle. The covenant was sworn in the name of the Lord, with the Lord standing between them, and it binds Jonathan and David and their descendants forever.
It was spoken as Jonathan's last words at their painful separation, when the two wept together and embraced before going their different paths. Jonathan sent David away in peace on the strength of that mutual oath even while Saul's murderous anger forced David's flight and shadowed both young men. God used Jonathan to help preserve David's life when Saul tried to kill him, and the sacred bond of the covenant remained unbroken through Saul's death.
In the covenant David promised Jonathan that when he should have rest from his enemies he would show kindness to the house of Saul. In his prosperity David remembered the covenant and asked if any were left of the house of Saul that he might show kindness for Jonathan's sake. He fulfilled it toward Jonathan's son Mephibosheth, who had been lame from childhood, by restoring Saul's private possessions for the support of his household and making him a constant guest sitting daily at the royal table. That generous and continued kindness overcame Mephibosheth's prejudice against David as a usurper, won his heart, and made his interest one with the king God had chosen, like his father Jonathan.