[Ruling on minor lying that entails no harm]

Answer: The reality of lying is that you promote your statement to the listener such that the listener believes its truth and correctness. On this basis, speech made in jest is not described as lying, because the report is not thereby promoted to the listener nor does he believe it to be true—the jest itself is an indicator that prevents that.
As for His saying—relating the words of Abraham (peace be upon him): “Rather, this—his largest—did it” [Al-Anbiyāʾ:63]—it is speech intended to expose the ignorance of idol-worshipers and to proclaim the feebleness of their minds, followed by arguing against them and compelling them: whoever cannot even break idols, how could he do anything greater than that? There is nothing in Abraham’s words that even suggests a lie, let alone constitutes one; rather, it is a kenning (kināyah) for what we have mentioned, and it contains lofty eloquence—since a kināyah can be more forceful than plain speech, in addition to the many meanings it conveys with few words. Therefore, this sentence is not among instances of lying, contrary to what is in some narrations—that Abraham (peace be upon him) told three “lies,” of which this was the last and the second was “Indeed, I am ill,” etc.
As for His saying: “Indeed, I am ill” [Aṣ-Ṣāffāt:89], it is not lying, as has been related concerning Abraham (peace be upon him). Rather, the meaning is: “I am sick at heart because of your worship of idols—dissatisfied with it, not agreeing to it, indeed utterly detesting it—since you have abandoned worship of the Lord of the worlds and turned to worshiping idols.”
The proof for what we have stated in this interpretation is that Allah, Exalted is He, said after “Indeed, I am ill”: “So they turned away from him, departing.” [Aṣ-Ṣāffāt:90] Allah related that they turned away from Abraham and rejected his idea and his call. Had it been—as in some narrations—that Abraham informed them of bodily illness, it would have sufficed for Allah to say “So they turned away,” and then “departing” would not add benefit. And Allah knows best. Thus the speech is figurative, its relation being the resemblance between the ailments of hearts and those of bodies.
As for His saying: “Indeed, you are thieves” [Yūsuf:70], it has been said that the brothers of Joseph (peace be upon him) had indeed committed a theft before; so Joseph called them “thieves” on that account, and this statement was not a lie.
As for the question, “Is lying permissible for a benefit?”—we say: If telling the truth entails a harm, then lying is permissible in that case—indeed, it may be obligatory. For example, a tyrant asks you about a believing man whom he wants to kill or torment with imprisonment, beating, or humiliation. It is obligatory for you to say, “I do not know where he is,” even if you do know his location. Indeed, if the tyrant makes you swear regarding what you say, you should swear that you do not know, and in that case you are truthful in your oath and not taken to task for it. The scholars, however, have mentioned that in such a case it is recommended for the one swearing to intend an internal interpretation (taʾwīl) of his oath—such as intending, “I do not know where he is—whether at the head of the gathering, or in the middle, or at the end,” or the like—so that he is truthful in his statement and his oath. What the scholars mentioned is fine and good; it contains prudence and safety. Yet such taʾwīl may not be feasible for common people, especially at moments of distress and pressure from the tyrant and the like.
If the speaker or the one swearing is able to employ such a taʾwīl, then it is better that he do so; otherwise there is no blame upon him, if Allah wills. This is an example of a situation in which lying is permissible.
Another example: where telling the truth would produce a greater harm than that of lying—such as a man engaged in reconciling two parties. He is asked about something and finds no escape from answering; yet if he answers truthfully it will intensify and inflame the discord, whereas if he answers contrary to the truth it will be more conducive to reconciliation. In this case, it is not permissible for him to tell the truth; rather, lying is the determinate course—if no indirect wording (maʿārīḍ al-kalām) is feasible for the speaker.
As for lying without any motive other than (personal) benefit, it is not permissible merely for the sake of benefit. Yes: lying in cases like the two examples above is good and does not nullify wuḍūʾ; but lying for mere (personal) benefit does nullify wuḍūʾ—this according to the position of the school and those who agree with them.
Source : Min Thimār al-ʿIlm wa al-Ḥikmah vol.1