Ruling 1586 — Fasting (Ṣawm)

If someone does not take due care and dust, smoke, or suchlike enters his throat, in the event that he was certain or confident that it would not reach his throat, his fast is valid; but if he only supposed (i.e. had ẓann) that it would not reach his throat, it is better that he keep a qaḍāʾ fast for it.