What is the ruling on taking money obtained from a lottery, and is it permissible to donate it to a sister to buy a house?

If the lottery means lottery contests, then it is a type of forbidden gambling and speculation, and its winnings are ill-gotten gains that are not permissible to own or benefit from. One must dispose of it by spending it on public interests or for the poor and needy.

If the sister is poor or needy, there is no objection to giving her what suffices her from this money, to the extent of her need, with the intention of getting rid of unlawful money, and not as charity or a gift.

As for buying a house for the sister, it is not permissible to spend money for this purpose unless she does not own adequate housing for herself and her children, even by renting. In this case, a full year's rent can be paid for her from this money.