Direct discourse reports what someone said with an exact quote. Biblical authors almost always never intend exact quotation. They use indirect discourse, reporting the basic content of what's said rather than the actual words used. When the biblical author is reporting in translation (as most of the gospel accounts do), this is even a translation of a summary of the actual words.
There's a common way of reporting indirect discourse by summary in the Hebrew scriptures that the ESV handles by expressions like "thus and so". It usually occurs to avoid repetition. Biblical Hebrew often reiterates something very closely for emphasis or for structural reasons. Sometimes it does so to show that a prophecy or command is being fulfilled exactly as given. But sometimes the author sees no need to repeat everything again. So you'll see these cases where someone will be told something who then reports it to someone else, and the second occurrence is something like, "and he told me thus and so". I noticed an interesting occurrence where that may be going on, but it may be something else.
1 Then Elisha the prophet called one of the sons of the prophets and said to him, "Tie up your garments, and take this flask of oil in your hand, and go to Ramoth-gilead. 2 And when you arrive, look there for Jehu the son of Jehoshaphat, son of Nimshi. And go in and have him rise from among his fellows, and lead him to an inner chamber. 3 Then take the flask of oil and pour it on his head and say, 'Thus says the Lord, I anoint you king over Israel.' Then open the door and flee; do not linger."
4 So the young man, the servant of the prophet, went to Ramoth-gilead. 5 And when he came, behold, the commanders of the army were in council. And he said, "I have a word for you, O commander." And Jehu said, "To which of us all?" And he said, "To you, O commander." 6 So he arose and went into the house. And the young man poured the oil on his head, saying to him, "Thus says the Lord, the God of Israel, I anoint you king over the people of the Lord, over Israel. 7 And you shall strike down the house of Ahab your master, so that I may avenge on Jezebel the blood of my servants the prophets, and the blood of all the servants of the Lord. 8 For the whole house of Ahab shall perish, and I will cut off from Ahab every male, bond or free, in Israel. 9 And I will make the house of Ahab like the house of Jeroboam the son of Nebat, and like the house of Baasha the son of Ahijah. 10 And the dogs shall eat Jezebel in the territory of Jezreel, and none shall bury her." Then he opened the door and fled.
11 When Jehu came out to the servants of his master, they said to him, "Is all well? Why did this mad fellow come to you?" And he said to them, "You know the fellow and his talk." 12 And they said, "That is not true; tell us now." And he said, "Thus and so he spoke to me, saying, 'Thus says the Lord, I anoint you king over Israel.'" 13 Then in haste every man of them took his garment and put it under him on the bare steps, and they blew the trumpet and proclaimed, "Jehu is king."[II Kings 9:1-13, ESV]
In verse 12, Jehu uses an expression that for all I can tell can be an instance of the above phenomenon. The author may simply be saving us some time by not reiterating everything the prophet had told Jehu, and the sense is that Jehu explained it all to them but that we're not going to have to hear it all explicitly. So when he says, "Thus and so he spoke to me" it means he actually told them the prophet's words or summarized them more fully than we see, but we only get "Thus says the Lord, I anoint you king over Israel". We're getting discourse within discourse. The author is reporting what Jehu says, and Jehu is reporting what the prophet had said, and it's possible the "thus and so" is an abbreviation of what Jehu says.
On the other hand, it seems just as possible to me (and perhaps the Hebrew precludes either option, but I don't know enough to know about that) that the "thus and so" is intended more like a direct quote from Jehu, and he is using it himself to abbreviate what the prophet said. Jehu has already shown his reluctance to tell his army buddies what went on, so it wouldn't be surprising for him to brush off their question by a quick summary, giving them the basic point that he's now been anointed king but leaving aside his responsibility to eliminate Ahab's house and the specific details of what will happen to Jezebel.
So if this expression is functioning the way I think it's functioning, then there's no semantic reason to prefer seeing it as Jehu's abbreviation of what the prophet said in order to brush off their question or the author's abbreviation of what Jehu said in order to spare us the repetition. There may be contextual clues that make one more likely, but it seems to me to be a semantic ambiguity that stems from the particular way this expression functions, and the Hebrew language (as far as I know) lacks a modifier to tell us whether direct or indirect discourse is going on, and so we can't (again, as far as I know) be sure just from the grammar which is intended. It does slightly affect the interpretation of the passage, since it may be another instance of Jehu's reluctance to embrace the kingship and/or his mission to eliminate Omri's dynasty, or it may just be an instance of the narrator sparing us a speech that repeats what we'd just heard.
If anyone who knows Hebrew has any information that helps here, I'd love to hear it.