Najis Clothes
Question :

If time is short and I know my clothing is najis, should I make the dress tahir and then make the prayer up afterwards or should I just ensure that I perform the prayers first so as to not make it qadha and then wash my clothes?

Answer :

If the only clothing available is najis, offering the prayer in such clothing is valid in cases of cold weather or similar necessities. If it can be taken off, the prayer should be offered twice, once with it and once while naked, based on compulsory precaution.
The mentioned necessity rarely occurs in our time since making use of a covering material during prayer is easily done. If not usual clothing, it can be anything like sheets, blankets or similar things as long as the private parts (as defined by the Sharia) are covered for the males and all parts of the body that must be covered for females are covered.