As far as fasting is concerned, what is the status of a sick person who does not know when he will recover? Should he fast? Should he make the intention for fasting?

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, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

The sick person is allowed to break his fast, but when he recovers, he is required to make up for the days that he has missed. Allaah, the Exalted, says (what means): {… So whoever among you is ill or on a journey [during them]—then an equal number of days [are to be made up]…} [Quran 2:184]. This is the case if the person's illness is ordinary and curable, regardless of when exactly recovery may take place. The person's ignorance of the time of his recovery does not affect the ruling as it is Allaah alone who cures illnesses. Once he recovers, the person is required to make up for the fasting that he missed, and he does not have to provide food as a compensation.

If, however, the person's illness is incurable, then he may break his fast and feed a poor person for each day of fasting that he has missed, as Allaah, the Exalted says (what means): {… And upon those who are able [to fast, but with hardship]—a ransom [as substitute] of feeding a poor person [each day]…} [Quran 2:184] He is required to provide a mudd of foodstuff on account of each person. The mudd weighs about 750 grams.  

Allaah Knows best.