Flavius Josephus, Antiquities of the Jews
William Whiston, A.M., Ed.

[229] But Jonathan heard these last words with indignation, and promised to do what he desired of him, and to inform him if his father's answers implied any thing of a melancholy nature, and any enmity against him. And that he might the more firmly depend upon him, he took him out into the open field, into the pure air, and sware that he would neglect nothing that might tend to the preservation of David; and he said, "I appeal to that God, who, as thou seest, is diffused every where, and knoweth this intention of mine, before I explain it in words, as the witness of this my covenant with thee, that I will not leave off to make frequent trims of the purpose of my father till I learn whether there be any lurking distemper in the most secret parts of his soul; and when I have learnt it, I will not conceal it from thee, but will discover it to thee, whether he be gently or peevishly disposed; for this God himself knows, that I pray he may always be with thee, for he is with thee now, and will not forsake thee, and will make thee superior to thine enemies, whether my father be one of them, or whether I myself be such. Do thou only remember what we now do; and if it fall out that I die, preserve my children alive, and requite what kindness thou hast now received to them." When he had thus sworn, he dismissed David, bidding him go to a certain place of that plain wherein he used to perform his exercises; for that, as soon as he knew the mind of his father, he would come thither to him, with one servant only; "and if," says he, "I shoot three darts at the mark, and then bid my servant to carry these three darts away, for they are before him, know thou that there is no mischief to be feared from my father; but if thou hearest me say the contrary, expect the contrary from the king. However, thou shalt gain security by my means, and shalt by no means suffer any harm; but see thou dost not forget what I have desired of thee in the time of thy prosperity, and be serviceable to my children." Now David, when he had received these assurances from Jonathan, went his way to the place appointed.