Is it permissible to seek treatment with one who claims that he has dealings with a doctor from among the Muslim jinn?

Firstly: 

It is not permissible to seek the help of the jinn for medical treatment or anything else, and it is not permissible to go to one who claims to do that. 

The Muslim should not be deceived by the success of anyone’s treatment or seeing the effects of that, for the Dajjaal will tell the sky to rain and it will rain, and he will tell the earth to bring forth its treasure and it will do so. Should the Muslim be deceived by him and believe his claims? It may be a test or a gradual punishment from Allaah. “We shall gradually seize them with punishment in ways they perceive not” [al-A’raaf 7:182].  

Shaykh ‘Abd al-‘Azeez ibn ‘Abd-Allaah ibn Baaz (may Allaah have mercy on him) was asked about the ruling on using the services of Muslim jinn to treat disease if that is needed. He replied: 

The sick person should not use the services of the jinn for treatment or ask them for anything, rather he should ask well known doctors, but he should not turn to the jinn, because that is a means that leads to worshipping them and believing them. Among the jinn are some who are kaafirs and some who are Muslims, and some who are innovators, and you do not know about them. So you should not rely on them or ask them for anything, even if they appear to you. Rather you should ask the people of knowledge and human doctors. Allaah condemned the mushrikeen as He said (interpretation of the meaning): 

“And verily, there were men among mankind who took shelter with the males among the jinn, but they (jinn) increased them (mankind) in sin and transgression”
[al-Jinn 72:6]

And it is a means that leads to dependence upon them and shirk, and it leads to seeking benefit from them and seeking their help, and all of that is shirk. End quote. 

Majallat al-Da’wah (no. 1602, Rabee’ al-Awwal 1418AH, p. 34) 

Shaykh Saalih al-Fawzaan (may Allaah preserve him) said: 

The help of the jinn should not be sought, whether from the Muslims among them or those who say that they are Muslim, because he may say that he is Muslim but he is lying in order to interfere with people. This should be prevented from the outset. It is not permissible to seek the help of the jinn even if they say that they are Muslims, because this opens the door to trouble. 

It is not permissible to seek the help of one who is absent whether he is a jinni or otherwise, and whether he is a Muslim or not. Rather we should seek the help of one who is present and is able to help, as Allaah said of Moosa (interpretation of the meaning): 

“The man of his (own) party asked him for help against his foe”

[al-Qasas 28:15]

Moosa was present and able to help, and it was possible for him to help as this was an ordinary situation. End quote 

Al-Sihr wa’l-Sha’wadhah, p. 86, 87 

Secondly: 

With regard to fasting, it is valid in sha Allaah and is not invalidated by that, although the reward for fasting may be reduced and may be erased altogether by the commission of sin. See the answer to question no. 50063. 

And Allaah knows best.