Should missed Sunnah prayer be made up?
Making up missed voluntary acts of worship is from Sunnah.
What is the ruling on performing istinja' after passing wind from the anus?
Ablution is invalidated by passing wind from the anus, even without a smell. Only ablution becomes obligatory from it. Istinja' is not obligatory nor recommended. And Allah the Almighty knows best.
Is fidyah required for someone who breaks their fast due to a valid excuse?
● If the excuse is permanent, such as a chronic illness with no hope of recovery or old age, then fidyah is required. This means feeding one needy person for each missed fasting day.
● However, if the excuse is temporary, such as menstruation, postnatal bleeding, or a temporary illness, then only making up the missed fasts (qada) is required, and fidyah does not apply.
Is it permissible to combine and shorten prayers at home before traveling?
It is impermissible to combine and shorten prayers at home before traveling because a person is called a traveler once he/she departs the borders of his/her country, and offering prayer that way was originally intended to exempt a traveler. And Allah Knows Best.