Day Questions

Given the death of every creation is predestined, is it permissible to smoke tobacco, for example, which decreases one’s lifespan?

As long as the individual is able to refrain from what could cause his death, he should protect himself. If he did not and performed what led to his death, he will be held accountable for making such decisions. One’s pre-destined death by Almighty Allah does not make him unaccountable for such negligence towards himself, as long as he is able to prevent himself from the causes of death.

There was a time when I had no knowledge about taharah. Must I repeat the prayers I performed during that time?

If you did not know that the wudhu was invalid because of the najasah then the prayer is correct.