Is it permissible to work in usurious banks in Islamic countries, especially if the work is not directly related to usury and it is the sole source of income?

Working in usurious banks is absolutely forbidden, even if the work is not directly connected to usury, such as security or cleaning, because that is considered aiding in consuming usury, writing it, and bearing witness to it.

The Permanent Committee for Scholarly Research and Ifta has issued a fatwa stating that a Muslim's work in a usurious bank is impermissible because it provides assistance to those involved in usury in their work, citing the verse: "And do not cooperate in sin and aggression" (Al-Ma'idah/2).

It further clarified that all those working in usurious banks are partners in sin, citing the hadith narrated by Jabir (may Allah be pleased with him) that the Prophet (peace be upon him) "cursed the consumer of usury, its client, its scribe, and its two witnesses, and he said: 'They are all equal (in sin).'"

Moreover, Sheikh Ibn 'Uthaymeen emphasized the prohibition of working in usurious institutions, even for a driver or a guard, because it necessitates approval of it, and whoever approves of what is forbidden incurs some of its sin.

Therefore, your husband must repent and leave this job, relying on Allah, who provides for those who fear Him from where they do not expect.