Is it forbidden to deal with a German company that turned out to be a Jewish company registered in Israel after completing a purchase, and is it permissible to remain in contact with it until the warranty period for the purchased devices expires?

The basic principle in dealing with disbelievers, whether in buying, selling, or other transactions, is permissibility. The Prophet, peace and blessings be upon him, used to deal with them. He bought food from a Jew and mortgaged his shield, and he dealt with the people of Khaybar on the condition that they cultivate the land and receive half of its produce.

It is stated in the fatwas of the Permanent Committee that merely eating with a disbeliever, sitting with him, or engaging in commercial transactions with him (buying and selling) does not lead to apostasy from Islam. Furthermore, showing kindness and doing good to disbelievers is not a sin as long as they have not fought Muslims regarding their religion and are not at war with them. Allah Almighty says: "Allah does not forbid you from those who do not fight you because of religion and do not expel you from your homes — from being righteous toward them and acting justly toward them. Indeed, Allah loves those who act justly."

Therefore, the mere fact that a company is Jewish does not prohibit commercial dealings with it.