Rashi on II Samuel
1 א

והנה איש בא מן המחנה. יש בפסיקתא שזה דואג ואינו מיושב על לבי:

Behold a man came from the camp. The Pesikta1Pesikta Rabosi 12,9. brings an opinion that this man is Doeig,2Doeig HaEdomi is first mentioned in Shmuel 1,21:8. but the explanation is indefensible in my heart.3It is clear from Shmuel 1, 22:18 that Shaul knew Doeig. Therefore, if in fact this man is Doeig, why did Shaul have to ask later in v. 8, “Who are you?” (Seder Hadoros, p. 102).