Is it permissible to sell accounting and warehouse management software to a library owned by a deviant who slanders the Companions and the wives of the Prophet, knowing that he sells books specific to their corrupt creed? And is doing so considered aiding in the spread of his corrupt belief, even though they are only sold to his followers?

It is impermissible to sell software to anyone known to use it for acts of disobedience (maʿṣiyah), such as usurious banks or for selling books that contradict the creed of Ahl al-Sunnah wa al-Jamāʿah. This is because such an act constitutes cooperation in sin and aggression, in accordance with the Almighty’s saying: (And cooperate in righteousness and piety, but do not cooperate in sin and aggression). The jurists have stipulated the impermissibility of selling or leasing anything known to be used for acts of disobedience, anything intended for unlawful purposes, and any transaction that leads to disobedience is forbidden. A Muslim must fear Allah and seek lawful sustenance. For whoever abandons something for the sake of Allah, Allah will compensate him with something better.