Is it permissible to lie to a sister who is mentally and physically ill to bring joy to her heart and prevent her from grieving, knowing that this lie is intended to alleviate her suffering and not to harm her?

The default ruling for lying is prohibition, except in specific cases for a benefit or to avert harm. However, one should not be lax in this regard.

Because lying is grave and its sin is great, and there is an alternative in ma'areed (allusive speech) to avoid it, whoever can do without lying by using tawriya (equivocation) and ma'areed is more deserving and better. Umar ibn al-Khattab, may Allah be pleased with him, said: "Indeed, in the allusions of speech, there is enough to spare a man from lying."

Ma'areed is speech that the listener understands to mean one thing, while the speaker intends something else. An example is Umm Sulaym's statement to Abu Talha about their sick son: "His breathing has calmed, and I hope he has found rest," where Abu Talha understood recovery, but she meant his death.

Therefore, ma'areed can be used with a sick person if telling the truth would negatively affect their illness. For example, you could say about your mother, "She is present," meaning she is present in this world, while she understands that she is at home. However, if telling the truth would not affect her, then the truth must be told.

Amusing stories and entertaining games can also be used for the patient.