Is it permissible to adopt the sick son of the wife's sister in a European country for the purpose of his treatment and improvement of his conditions, knowing that adoption is forbidden in Islamic law, and with the intention of returning him to his family when his condition improves?

Adoption is forbidden due to the harms it entails, including lying, circumventing state laws, violating the necessary conditions for residency, and the child taking what is not due to him except as a true son. His current situation is not considered a necessity that permits this forbidden act. It is advisable to seek another way to treat him without falling into the forbidden, such as bringing him in with a visa.