Question Summary:
Is ghusl compulsory if a person emits semen without ejaculating or by blocking the semen?

Question Detail:

If you emit semen without ejackulating, need to make ghusul? How about if you ejackulate but block it. And why?

Answer :

In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
What do you mean by semen? There are three types of fluids which are discharged:
1.      Mani (seminal discharge)
2.      Mazi (discharges due to arousal or excitement)
3.      Wadi (emission generally after urinating)
If by semen you are referring to mazi or wadi, then ghusl is not required. These discharges emit gradually. [1]
If by semen you are referring to mani, and it emits without ejaculation or without passion, ghusl is also not required in this case. [2]
However, if semen emits with ejaculation or with passion but one manages to prevent it from coming out at that moment, and it comes out later, then one will have to perform ghusl after it comes out. [3]
 
And Allah Ta’āla Knows Best
Abdul Hannan Nizami,
Student Darul Iftaa
Chicago, USA
Checked and Approved by,
Mufti Ebrahim Desai.