Question: Is it permissible for Muslim lawyer to write a will for a non-Muslim client in accordance with the English law since the non-Muslim may have bequeathed some or all of his wealth to such institutions which may either be unknown or even prohibited like the institutions for caring of dogs or sailors?
1: If the transaction is between a Kafir client and a Muslim lawyer, it is a matter of hiring for the purpose of writing a will for the kafir as dictated to by the client to the Muslim writer hired for this purpose. Thus it is a contract of hiring (ijara) for writing the will. The lawyer writes the will as the kafir tells him to write and then the lawyer takes his wage and the relations ends there so far as the will is concerned...
If the matter is such then it is permitted with condition that nothing in contravention to the Islamic ‘Aqeedah is mentioned in the will because writing of anything in violation of the Islamic ‘Aqeedah is similar to pronouncing such a thing and that is not permissible.
However it is preferred not to write such a will so long as it contains matter which goes against the commands of Islam. This is to distance oneself from appearing to agree with such clauses appearing in the will of the kafir.
2: However if the transaction between the owner of the will and the lawyer happens to a deal of representation (wakalah), i.e. the lawyer represents the owner of the will and executes his will...he contacts the concerned persons, informs them of the will and executes the process in his capacity as representative of the owner of the will... then this is not permitted because in such a condition the Muslim lawyer executes a will in violation of the Islamic Shari'ah in which a Muslim believes.