It is Makrooh-e-Tahrimi to perform oral sex. Firstly, these are places of the body through which impure things come out. How then is one willing and desiring to place his or her mouth on such a place. It's quite against humanity. If one argues that these impurities do not enter the mouth then I will say indeed they do. Even if it is not performed to the extent of orgasm, still the impurity which proceeds 'Manee' that is called 'Mazee' is sure to enter the mouth. The 'Ulama are unanimous that 'Mazee' is Najis, filthy and Napaak and in no way should it enter the mouth which is the source of reciting the Qur'aan and taking Allah's name. One must abstain from this. There are other ways of fulfilling ones desires. Also, one must not take Makrooh-e-Tahrimi lightly. This is very close to Haraam and if one persistently performs a Makrooh-e-Tahrimi act then it becomes Haraam. Allamah Shami has stated this in his famous book on Fatwa.

Allah knows best.

Answer Approved by Shaikhul Hadeeth Mufti Farooq