Day Questions

Is it permissible to attend gyms that are used by both males and females, if we don't commit any forbidden act?

This is permissible in and of itself, but one should beware from committing sins when being there.

Is a father allowed to force his daughter to wear hijab if she refuses to wear it? In particular, is he allowed to: (a) use physical violence to force her to wear hijab? (b) withdraw his financial support from her as long as she doesn't wear it?

It is obligatory on the father to raise his children on religious teachings. He can use the moral power of fatherhood in order for them to be obedient to the teachings of Islam. Amongst those teachings is the hijab. This can be achieved by moral pressure and continuous advice especially if it is associated with strong relationship between the father and his daughter, based on love, respect and fatherly compassion.

When giving the Kaffara, do I have to feed all sixty people at once or can I feed one every day or the like?

It is obligatory to give to sixty people for every day you have missed whether by giving food to them all in one day or over a longer period.