Cosmetic surgery to reduce the thighs
Question

With regard to surgery to reduce the thighs, posterior and breasts – is it haram or halaal, if it is essential?.
Praise be to Allah.Some kinds of cosmetic surgery are permissible and some are haram. That depends on the motive for doing this surgery. If the motive is to look beautiful or increase beauty, then the scholars regard this type of surgery as changing the creation of Allah and tinkering with it according to people’s whims and desires, so it is not permissible to do that, as was stated by Shaykh Muhammad al-Mukhtaar al-Shanqeeti in his book Ahkaam al-Jiraahah. That is based on the following evidence:
1 – Allah tells us that Iblees (may the curse of Allah be upon him) said (interpretation of the meaning): 
“and indeed I will order them to change the nature created by Allah”[Al-Nisa’ 4:119]. 
2 – ‘Abd-Allah ibn Mas’ood (may Allah be pleased with him) narrated that he heard the Messenger of Allah (peace and blessings of Allah be upon him) curse the women who pluck their eyebrows and file their teeth for the purpose of beautification, who change the creation of Allah. Narrated by al-Bukhari (4507). 
3 – This surgery is only done by doing other things that are forbidden in sharee’ah, such as anaesthesia which is basically haram unless there is a need for medical treatment.  
Those haram things also include uncovering and touching the ‘awrah. All of these things are haram and there is no acceptable shar’i reason for granting a concession with regard to them. 
But if the aim of this operation is to remove a fault, such as if the buttocks  or breasts are abnormally big, and the aim is to put them back to normal, then there is nothing wrong with doing this surgery. For more information please see the answer to question no. 47694. 
Al-Nawawi (may Allah have mercy on him) said in his commentary on Saheeh Muslim, when commenting on the hadeeth of ‘Abd-Allah ibn Mas’ood (may Allah be pleased with him) about the Messenger of Allah (peace and blessings of Allah be upon him) cursing women who do tattoos and those who have them done: With regard to the words “and women who file teeth”, what is meant is that they do that for the purpose of beautification, which indicates that what is haram is that which is done for the purpose of beautification, but if there is a need for that as a remedy or because of a fault in the teeth and the like, there is nothing wrong with it.  
Shaykh Ibn ‘Uthaymeen (may Allah have mercy on him) said: Removing faults is permissible. Hence the Prophet (peace and blessings of Allah be upon him) allowed the one whose nose had been cut off in battle to wear a nose made of gold. The matter is broader in scope than that, as it also covers issues of beautification and cosmetic surgery. That which is done to remove a fault is permissible, such as if a person has some crookedness in his nose and he straightens it, or he removes a black spot, for example. There is nothing wrong with that. But if it is not done to remove a fault, such as tattooing and plucking eyebrows, for example, then this is forbidden. End quote from Majmoo’ al-Fatawa (11/93). 
And Allah knows best.