It is narrated from Imam Baqir (AS) who said:

The believer is continuously inflicted with grief and sorrow in order that there is no sin is left for him/her [1]. In another narration, Imam Baqir (AS) said: When God wants to show kindness and mercy to a sinful servant, will inflict him/her with illness and if this is not done, that person will be made poor and needy, and if this is not done, God will make passing away hard for such a person in order to forgive his/her sins. On the other hand, God grants healthy body to a person who has done good deeds, and if that is not done, his/her sustenance will be increased, and if this is not done, death will be easy for such a person in order for that person to be rewarded in this world and he/she has nothing to ask God in this regard in the hereafter [2].

[1] Osul Kafi, Vol. 4, Page 182.

[2] As Above, Page 179.

Source: en.shafaqna.com