Assalamu alaikom,
I have read many fatwas ,which say that water vapor ,if inhaled, invalidates the fast.So my question is that I was fasting one day and I was reheating some food leftovers to avoid spoilage.As I was doing so,I bent down and started smelling it (while the vapor was coming out) to find out if didn't spoil already.When I did this ,I had completely forgotten the ruling regarding inhaling water vapor.It entered my nose ,but I am not sure f any water drops formed down my throat.So is my fast invalidated in this case and should I make up this day now?Thank you for your time.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.

The scholars differed in opinion whether or not inhaling vapor invalidates the fast. However, even according to the opinion that vapor breaks the fast, your fasting is correct and you are not obliged to make it up for the following two reasons:

1-     You are not sure that the vapor reached your throat or stomach, so in principle the fasting is valid and it is not invalidated just because of doubt; this is because the well-known Fiqh rule reads: “Certainty is not overruled by doubt.”

2-     If we presume that some vapor reached your throat, you did so out of forgetfulness –as it appears from the question –and whoever eats or drinks out of forgetfulness, his fasting is not invalidated according to the correct opinion of the jurists . Therefore, your fasting is correct, Allaah willing.

For more benefit, please refer to Fatwa 85377.

Allaah Knows best.