Is it permissible for me to design a website for a company that helps clients obtain interest-based loans, knowing that the company does not provide the loans itself but rather assists in finding them? And would my refusal of this job, on the grounds that my cousin is not Muslim, give a bad impression of Muslims?

It is permissible for a Muslim to work in designing permissible websites, while avoiding the design of forbidden websites, in accordance with the Almighty’s saying: (And do not cooperate in sin and aggression).

If the company's work is mostly permissible, and some of its activities are forbidden, such as usury, then it is permissible to design a website for it, provided two conditions are met:

1. The majority of the company's work must be permissible, not forbidden. 2. The designer must not perform any work related to the forbidden activity or that indicates it.

As for informing the cousin of the Sharia ruling, it is an invitation to Islam, and a Muslim's failure to adhere to it harms Islam; because seeking people's pleasure by incurring Allah's wrath leads to harm, as stated in the Hadith: "Whoever seeks the pleasure of Allah at the expense of people’s displeasure, Allah will suffice him against people. And whoever seeks the pleasure of people at the expense of Allah’s displeasure, Allah will entrust him to people." The true invitation to Islam is by adhering to it, not by words that contradict actions.