Supplication is from the most beneficial types of healing, it is the enemy of illness and affliction - repressing it and treating it, preventing its occurrence, removing it or at least alleviating it. It is the weapon of the believer as is reported by al-Haakim in his 'Mustadrak' from the hadeeth of Alee bin Abee Taalib (RA) from the Messenger of Allaah sallallaahu 'alayhi wa sallam that he said, "Supplication is the weapon of the believer, the pillar of the religion, and the light of the heaven and earth." (Abu Ya`laa)
Supplication takes one of three positions against illness:
It is stronger than the illness and therefore represses it.
It is weaker than the illness and therefore the illness overcomes it and afflicts the servant, however it is still possible that it alleviate the illness.
That they be of equal strength and prevent each other from happening in the servant.
Al-Haakim reports from the hadeeth of Aa`ishah (RA) that the Messenger of Allaah sallallaahu 'alayhi wa sallam said, "Caution is of no avail against the decree but supplication benefits those things that have occurred and have not yet occurred. For indeed while the tribulation is descending the supplication meets it and they remain struggling with one another until the Day of Judgement." (Haakim, at-Tabaraanee)
He also reports the hadeeth of ibn Umar from the Messenger of Allaah sallallaahu 'alayhi wa sallam that he said, "Supplication brings about benefit to those things that have occurred and those things that have not yet occurred. So devote yourselves to supplication O servants of Allaah!" (Mishkaat al-Masaabeeh)
He also reports the hadeeth of Thawbaan from the Prophet sallallaahu 'alayhi wa sallam that he said, "Nothing but supplication averts the decree and nothing but righteousness increases the life-span. Indeed a person is deprived of provision due to performing sins." (Mishkaat al-Masaabeeh)
