Ruling on treating the sick person by slaughtering a sheep for the sake of Allaah
Question

Is treating the sick person by slaughtering ( an animal) purely for the sake of Allaah permissible or not? Because I decided, after praying istikhaarah, that I should treat sickness caused by sihr (witchcraft), the evil eye and jinn possession, by offering a sacrifice purely for the sake of Allaah, in which I say my du’aa’ when offering the sacrifice: “O Allaah, accept it from Your slave, So and so the son of So and so, as You accepted it from Your slave and Your Prophet Ibraaheem (peace be upon him), and make it sincerely for Your sake. O Allaah, it is from You and to You.” I want to follow the words of the Messenger (blessings and peace of Allaah be upon him): “Treat your sick ones with charity, purify your wealth with zakaah, and respond to calamity with supplication and beseeching of Allaah.” And because the Prophet (blessings and peace of Allaah be upon him), when he was asked about ruqyah, said: “There is nothing wrong with ruqyah so long as it does not involve sin or shirk,” or words to that effect. I have found this way to be beneficial in treating disease, especially in the case of possession. Please advise us, may Allaah reward you: is treating sickness by means of offering a sacrifice permissible or not?.
Praise be to Allah.The part that is saheeh of the hadeeth mentioned by the questioner is “Treat your sick ones with charity.” This was classed as hasan by Shaykh al-Albaani in Saheeh al-Jaami’ (3358). But some scholars classed it as da’eef (weak) and did not think it was saheeh or sound. 
As for the extra material that was mentioned by the questioner, “and purify your wealth with zakaah,” al-Albaani said concerning it in al-Silsilah al-Da’eefah (3591): It is mawdoo’ (fabricated). 
The same applies to the additional material that follows it: “and respond to calamity with supplication and beseeching of Allaah.” Al-Albaani said in Da’eef al-Targheeb wa’l-Tarheeb (456): It is da’eef (weak). 
There is nothing wrong with the sick person sacrificing a sheep or the like in the hope that Allaah may heal him thereby from the pain and sickness he is facing, because charity is one of the means of healing. 
See the answer to question number 107549, where we quoted fatwas from the Standing Committee for Issuing Fatwas and Shaykh ‘Abd al-Rahmaan ibn Jibreen concerning that. 
But it should be noted that the charity mentioned in the hadeeth does not refer specifically to offering a sacrifice; rather it includes giving food, clothing, money and so on in charity. 
The supplication that the questioner mentions is not narrated in the Sunnah -- as far as we know -- so he should not adhere to that and believe that it has any superiority over any other supplication. 
It is prescribed for the believer to pray that his righteous deeds be accepted. “And (remember) when Ibraaheem (Abraham) and (his son) Ismaa’eel (Ishmael) were raising the foundations of the House (the Ka‘bah at Makkah), (saying), ‘Our Lord! Accept (this service) from us. Verily, You are the All-Hearer, the All-Knower’”
[al-Baqarah 2:127]. 
And Allaah knows best.