[When does a Muslim’s wealth become lawful for another to take or use?]

Answer: A Muslim’s wealth is not lawful (for another) except by his willing consent. Allah Most High says, “O believers! Do not devour one another’s wealth illegally, but rather trade by mutual consent.” [An-Nisāʾ:29]. And in the well-known ḥadīth: “Indeed, your blood, your honor, and your wealth are inviolable for you—like the sanctity of this day of yours …” ḥadīth.
- Scholars have allowed the ruler to take from people’s wealth what he uses to repel an enemy marching upon them. They permitted this because if that enemy is not repelled, he will take their wealth and commit atrocities; thus, it is permissible for the ruler to ward off that great evil and widespread harm by taking some of their wealth. Although that entails harm to them, it is a lesser harm compared to the harm of the enemy; and repelling a greater harm by means of a lesser harm is something whose soundness is firmly recognized by reason.
There is another situation in which it is permissible to eat from a Muslim’s wealth without his permission: when hunger reaches a person to the point that he fears death or serious illness harmful to his health. In that case, if he finds no other option, he may eat from a Muslim’s wealth without permission—but only what suffices to remove the necessity.

Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2