Shortening (of the prayer) is impermissible for the sick–it is only permissible for the traveler Allah the Most High says:
“And when you (Muslims) travel in the land, there is no sin on you if you shorten your Salaat” [an-Nisaa verse 101] Darb fel ‘Ard’ [i.e. means traveling].
As for combining the prayers in one of the two times, similarly combining of Dhuhr and ‘Asr and the combining of Maghrib and ‘Ishaa [in one of the times of prayer– early or later]. For verily it is permissible for the sick when is in need to combine prayers if it is lighter upon [ease], thus it is permissible for him to do so in this circumstance; but as for shortening the prayer– it is impermissible for the sick because he is a resident and it is impermissible for them to shorten the prayer– it has been made concession for the traveler only.
Fatwa given by Shaykh Saleh al Fawzan reference: al Mun’taqa vol. 2 page 221 question 274
Translation by: Abu Sulaymaan Muhammad Ibn Baker