Midrasch zu Divrej Hajamim I 12:19

(Fol. 62) R. Huna and R. Chisda were both sitting when G'niba, who was walking, passed near them. One said to his associate: "Let us arise before a scholar." The other remarked: "Let us arise before a quarrelsome man." Meanwhile G'niba approached them: "Peace unto ye, kings," said he to them. Whereupon they said to him: "Whence do you know that Rabbis are termed kings?" He said to them: "From the following passage, (Pr. 8, 15) Through me (the Torah) do kings reign," etc. "Whence do we know that we should repeat the bidding of peace unto a king?" they again asked him, whereupon he said to them: "Thus said R. Juda in the name of Rab, Whence do we know that we should repeat the bidding of peace to a king? It is said (I Chr. 12, 19) Then a spirit invested (Amasai) the chief of the captains, [who said]. Thine are we David, and with thee O son of Jesse! peace, peace be unto thee,'" etc. They then said to him: "Let the master taste something." Thus said Raba in the name of Rab," replied he: "It is prohibited for a man to taste anything before a man feeds his animal, for it is said (Deut. 11, 15) And I will give grass in thy field for thy cattle, and afterwards it is said, And thou shalt eat and be satisfied."

Behold, I send an angel before thee (Exod. 23:20). Scripture says elsewhere in reference to this verse: For He will give His angels charge over thee, to keep thee in all thy ways (Ps. 91:11). When a man performs one precept, one angel is assigned to guard him; when he performs two precepts, two angels are given to him; when he performs all the precepts, many angels are assigned to him, as it is said: For He will give His angels charge over thee. Who are these angels? They are the beings who will protect him from demons, as it is said: A thousand may fall at thy side, and ten thousand at thy right hand (ibid., v. 7). What is meant by may fall? It means that they force (their opponents) to surrender to him, as it is said in the Book of Chronicles: Of Manasseh also there fell away some to David (I Chron. 12:20), and it is written as well: As he went to Ziklag, there fell to him of Manasseh (ibid., v. 29).