Musnad Abu Ya'la al-Mawsili 147:52

Ibrahim ibn al-Hajjaj al-Sami narrated to us, Hammad narrated to us, from Sinan Abu Rabi'ah, from Anas ibn Malik, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "If Allah afflicts a Muslim with a trial in his body, He says to the angel: 'Write for him his righteous deeds that he used to perform.' If He heals him, He washes him and purifies him; and if He takes his soul, He forgives him and has mercy upon him."