Supplication is one of the most beneficial cures. It is the enemy of affliction, challenging and treating it, by preventing it from occurring; it removes it or weakens it if it falls upon a believer. It is the weapon of every believer, as reported by Al-Haakim in his Sahih book, on the authority of Ali bin Abi Talib (radiallaahu ‘anhu) that the Prophet (sallallaahu ‘alayhi wa sallam) said: “Supplication is the weapon of the believer; it is the pillar of Islaam, and the light of the heavens and the earth.”
There are three situations in relation to this affliction or trial:
First, when it is more powerful than the affliction so it drives it away.
Second, when it is weaker than the affliction, however it reduces its effect.
Third, when they resist each other and so each one prevents the other from being effective.
Abu Khizamah said: ‘O Messenger of Allaah, do the incantations that we invoke, the medicine that we apply, and the preventative measures that we observe avert, in anyway, the Decree of Allaah?’ He (sallallaahu ‘alayhi wa sallam) replied: ‘That is also a part of the Decree of Allaah (Al-Qadr). [Recorded by At-Tirmidhi, Ahmad and Ibn Maajah]
Thawbaan (radiallaahu ‘anhu) also reported that the Prophet (sallallaahu ‘alayhi wa sallam) said: “Only supplication averts the decree, only kindness prolongs life, and a man is deprived of provision for a fault he commits.” [ Recorded by At-Tirmidhi and Ibn Maajah]