What is the ruling of Islamic law on refraining from eating fruit sent by a relative who works in a garden, on the pretext that it was taken without the knowledge of his employers, and is this refraining considered an injustice to him? And what is the expiation for this injustice, if it exists?

The employee is not permitted to give away fruits from the garden without the owner's permission. If the person reporting on the employee's situation is trustworthy and reliable, then their report is to be believed and acted upon accordingly, whether it pertains to religious matters or reports regarding impurity, permissibility, and prohibition. Acting upon the report is not limited to refraining from eating the fruit, but also includes refraining from accepting it at all, and advising the employee and enjoining them from evil. Uttering "Bismillah" does not make something usurped or stolen permissible. However, if the informant is not trustworthy, their report should not be relied upon. There is no injustice in refraining from accepting a gift due to doubt about its permissibility; rather, injustice lies in falsely accusing someone.