Narrated Uqba bin Aamir: The Prophet (sallallaahu ‘alaihi wa sallam) said: Every deed of the day is sealed up. When a believer falls ill, the angels say: O our Lord! Your slave so-and-so has fallen ill. The Lord (‘Azza wa Jall) says: Note down to his credit the same deeds he was doing before illness, until he heals up or dies.
Sound Hadeeth reported by Ahmad in his Musnad