[Ruling on Delivering a Trust (Amānah) to One Who Will Use It to Wage War on Religion]

Answer—and from Allah is success: it is not permissible for the carrier of the trust mentioned in the question to deliver it to a party that wars against faith and religion, for that strengthens falsehood and its people, and due to His saying Most High: “And cooperate in righteousness and piety, but do not cooperate in sin and aggression.” [Al-Mā’idah:2]. One of two courses is incumbent upon the carrier of the trust:
1- Either to return it to its owner who gave it to him.
2- Or to hold it with him until its owner who gave it to him comes, and then return it to him.
If it is said: Why did you not say that he may give it toward the benefit of religion—to strengthen its side and to honor truth and its people? For when Allah Most High forbade cooperation upon sin and aggression, He commanded cooperation upon righteousness and piety—and strengthening and honoring religion are among the greatest forms of righteousness and piety.
We say: Allah has emphasized the matter of trusts; He said, Exalted is He: “Indeed, Allah commands you to render trusts to whom they are due.” [Al-Nisā’:58]. And in the hadith: “Trusts are to be rendered to the righteous and the wicked.” And what is well known in the Sīrah: when the Prophet (May Allah bless him and his family and grant them peace) emigrated from Mecca to Medina, he left ʿAlī (Peace be Upon Him) in Mecca to return the trusts that were with the Prophet (May Allah bless him and his family and grant them peace) to their owners, and the people of those trusts at that time were polytheists.
— Allah Most High has forbidden treachery and condemned its people in the Noble Qur’an. Indeed, it is not permissible to betray a trust even if it belongs to a hostile unbeliever at war, because your carrying the trust of the hostile unbeliever and your agreeing to carry it for him constitutes granting security to his property.
It has been established among the scholars of the Muslims since the time of the Companions that if any one of the Muslims signals to a hostile unbeliever at war and he approaches by that signal, that signal counts as granting him security—together with whatever he has of wealth, weapons, or the like. None may assault him or what is with him; then they must escort him back to a place of safety. In this there is proof for what we have mentioned of the inviolability of trusts—even if they belong to a hostile unbeliever at war.
If it is said: Is it permissible for the ruler or for other Muslims to seize the trust from its carrier because it belongs to those at war?
We say: rather, it is obligatory upon the ruler and others among the Muslims to assist the carrier of the trust in safeguarding it, due to the hadith: “The least of the Muslims grants protection on behalf of all of them, and they are one hand against others.” Thus, if the granting of security to the one at war issues from a single Muslim, it is as though it were security from all the Muslims.
If the trust the Muslim is carrying is wine, or an explosive device sent with the Muslim to a man ordered to blow up a mosque, or the house of a believer, or the like—and this does not become clear to the carrier until after he has taken it—then as for the wine, he pours it out or burns it; and as for the explosive device, he returns it to its owner, or he holds it with him until its owner comes, and then he returns it to him.
We distinguished between the two because the very substance of wine is prohibited; no use of it is permissible for us. As for an explosive device, its very substance is not prohibited; it may be used in multiple domains. What is prohibited for us is using it for sin and aggression.
Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2