What is the ruling if a brother asks his sister to lie to his wife; should the sister obey him or not, knowing that the brother is very obedient (to Allah) and fears Allah?

Lying is forbidden except out of necessity or need where the purpose cannot be achieved by a lawful means. It is permissible for reconciling people or for one spouse to please the other. The Prophet, peace and blessings be upon him, said: "He is not a liar who reconciles between people, narrating good or saying good." One may resort to ma'areedh or tawriyah, which is using a word that bears two meanings, where the speaker intends one of them that does not immediately come to mind. Every commendable matter that cannot be achieved except through lying is permissible, though tawriyah is preferable.