Some married couples like to do some sexual fantasies so they role play the master and the slave and this sex act could contain some sadism so one party can get hurt. So is this sexual fantasy prohibited or not?

Sadism indicates the tendency to derive pleasure and sexual gratification from inflicting pain, suffering or humiliation on others. This terminology was first used by the French writer Marquis De Sade (1740- 1814) who was known for his erotic and controversial literature which included a lot of violent sexual content.

It is well known that hurting the other party whether psychologically or physically in the sexual relationship or in any other relationship is legally prohibited. God says, “Say, My Lord has only forbidden immoralities - what is apparent of them and what is concealed - and sin, and oppression without right, and that you associate with Allah that for which He has not sent down authority, and that you say about Allah that which you do not know." 7:33

The Prophet also said, “Do not inflict harm” and preserving one’s life is one of the major objectives of the Isalmic Shari’ah. The renowned Muslim scholars believe that the Islamic Shari’ah with all its variant rulings revolve around preserving the five major objectives of Shari’ah which are preserving life, religion, dignity, mind and possession. It was narrated through ‘Abdullah ibn ‘Abbas that the Prophet said during the last sermon in pilgrimage, “O people your blood, money, and honors are forbidden” (Bukhari).

As for engaging in sexual acts in any position that the couple agree on is lawful as God says, “Your wives are a place of sowing of seed for you, so come to your place of cultivation however you wish and put forth [righteousness] for yourselves” 2:223

All sexual positions are permissible except for anal sex and also engaging in sex during the wife’s menstrual period is deemed impermissible. God says, “And they ask you about menstruation. Say, "It is harm, so keep away from wives during menstruation. And do not approach them until they are pure.” 2:222

Therefore all sexual acts are permissible except also for acts that are forced by one party on the other which might lead to repulsion and repugnance.