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

[226] Hereupon, when Jonathan found that this intention of Saul was so well attested, he asked him what he would have him do for him. To which David replied, "I am sensible that thou art willing to gratify me in every thing, and procure me what I desire. Now tomorrow is the new moon, and I was accustomed to sit down then with the king at supper: now, if it seem good to thee, I will go out of the city, and conceal myself privately there; and if Saul inquire why I am absent, tell him that I am gone to my own city Bethlehem, to keep a festival with my own tribe; and add this also, that thou gavest me leave so to do. And if he say, as is usually said in the case of friends that are gone abroad, It is well that he went, then assure thyself that no latent mischief or enmity may be feared at his hand; but if he answer otherwise, that will be a sure sign that he hath some designs against me, Accordingly thou shalt inform me of thy father's inclinations; and that out of pity to my case and out of thy friendship for me, as instances of which friendship thou hast vouchsafed to accept of the assurances of my love to thee, and to give the like assurances to me, that is, those of a master to his servant; but if thou discoverest any wickedness in me, do thou prevent thy father, and kill me thyself."