Ruling on one who thinks that sihr is OK so long as it does not cause any problems

Sihr is evil and is kufr. If a sick person is not cured by reading (Qur’aan and du’aa’s), then we should note that medicine does not guarantee a cure either, because not every treatment produces the desired result. Allaah may delay the healing for a long time, or the person may die from this sickness. It is not a condition of treatment that the person should be healed. If a person is treated by reading Qur’aan and does not recover, that is not an excuse for turning to sihr, because we are commanded to take the permissible means prescribed in sharee’ah, and we are forbidden to use haraam means. The Prophet (peace and blessings of Allaah be upon him) said, “O slaves of Allaah, seek treatment but do not seek treatment with that which has been forbidden to you.” And it was narrated that he (peace and blessings of Allaah be upon him) said: “Allaah does not make your healing in that which He has forbidden to you.” 

All things are in the hand of Allaah, may He be glorified. He is the One Who heals whomsoever He wills, and He decrees sickness and death for whomsoever He wills, as He says (interpretation of the meanings): 

“And if Allaah touches you with harm, none can remove it but He, and if He touches you with good, then He is Able to do all things” [al-An’aam 6:17]

 “And if Allaah touches you with harm, there is none who can remove it but He; and if He intends any good for you, there is none who can repel His Favour which He causes it to reach whomsoever of His slaves He wills. And He is the Oft-Forgiving, the Most Merciful [Yoonus 10:107]

 So the Muslim must be patient and seek reward with Allaah. He must limit himself to the means that Allaah has permitted, and beware of that which Allaah has forbidden, whilst also believing that the decree of Allaah is beneficial and that His command cannot be put back, as Allaah says (interpretation of the meanings):  

“Verily, His Command, when He intends a thing, is only that He says to it, ‘Be!’ and it is! [Yaa-Seen 36:82]

 “And you cannot will unless (it be) that Allaah wills the Lord of the ‘Aalameen (mankind, jinn and all that exists) [al-Takweer 81:29] 

And there are many similar aayaat.