[Ruling on Delivering a Trust to Someone Who Will Use It to Wage War Against Religion]

Answer—with success from Allah: It is not permissible for the carrier of the trust mentioned in the question to deliver it to the party that is at war with faith and religion; that would strengthen falsehood and its people. Allah Most High says, “Cooperate with one another in goodness and righteousness, and do not cooperate in sin and transgression.” [Al-Mā’idah:2]. In this case, the carrier of the trust must do one of two things:
1- Either return it to the one who gave it to him.
2- Or hold it with him until the one who gave it to him comes back.
If it is said: Why do you not say, “He may give it in the interest of the religion, to strengthen its side and to honor the truth and its people,” since when Allah forbade cooperating in sin and aggression, He commanded cooperating in righteousness and piety; and strengthening the religion and honoring it is among the greatest kinds of righteousness and piety?
We say: Allah has emphasized the matter of trusts, saying, “Indeed, Allah commands you to return trusts to their rightful owners.” [An-Nisā’:58]. And in the ḥadīth: “Fulfill the trust for the one who entrusted you, and do not betray the one who betrayed you.”
The well-known report in the Sīrah is that when the Prophet (May Allah bless him and his family and grant them peace) emigrated from Makkah to Madīnah, he left ʿAlī (Peace be Upon Him) in Makkah to return the trusts that were with the Prophet (May Allah bless him and his family and grant them peace) to their owners—even though the people of those trusts were, at that time, idolaters.
- Allah has forbidden treachery and condemned its people in the Noble Qur’an. It is not permissible to betray a trust—even if it belongs to a belligerent non-Muslim—because your carrying the trust of a belligerent and agreeing to carry it for him counts as granting safety to his property.
It has been established among the scholars of the Muslims since the time of the Companions that if any Muslim signals to a belligerent non-Muslim so that he comes to him at his signal, that counts as granting him security—for his person and for what is with him of wealth, weapons, or the like. It is then not permissible for anyone to assault him or what is with him; rather, they must return him to a place of safety.
This is proof of what we have mentioned: that a trust is inviolable—even if it belongs to a belligerent non-Muslim.
If it is said: May the ruler or other Muslims seize the trust from its carrier because it is the wealth of belligerents?
We say: Rather, it is obligatory on the ruler and other Muslims to assist the carrier of the trust in safeguarding it; for in the ḥadīth: “The protection granted by the lowest (in status) among the Muslims is binding upon them all, and they stand united against others.” Thus, if a non-Muslim combatant is granted security (a man) by a single Muslim, it is as if the security were granted by all Muslims.
If the trust the Muslim carries is wine, or an explosive charge sent with him to a man commanded to blow up a mosque or a believer’s house, or the like—and this does not become clear to the carrier of the trust until after he has already taken possession—then as for the wine, he pours it out or destroys it by burning; and as for the explosive, he returns it to the one who gave it to him or keeps it until that person comes, then returns it to him.
We only distinguished between the two because the very substance of wine is unlawful; we are not permitted any use of it. As for the explosive charge, its very substance is not unlawful; it has many permissible uses. What is unlawful for us is using it for sin and aggression.

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