When I defecate, then sometimes, due to pressure, some semen or a white fluid (it may be mathiy) comes out, without feeling any pleasure, so I just wash it off and continue as normal. I have got to know that the emission of semen without feeling pleasure does not necessitates ghusl (ritual bath), but I am worried and wonder whether if it is mathiy I have to make ablution immediately or can do it later on. Most probably, it is semen.

All perfect praise be to Allaah, The Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ʻalayhi wa sallam, is His slave and Messenger. 

The emission of semen (maniyy) without sexual arousal does not necessitate ghusl according to the majority of scholars, and this is also the chosen opinion in Islamweb.

The Kuwaiti Encyclopedia of Fiqh says, "Scholars unanimously agreed that the emission of semen necessitates ghusl if it is discharged with lust and comes out gushing. However, if it is discharged without lust and without gushing, then it does not necessitate ghusl according to the majority of scholars..."

The emission of semen without lust means that it has the smell and color of semen but no sexual pleasure is felt with its discharge; rather, it comes out due to sickness or cold or as a result of carrying something heavy, breaking your back, or other reasons. The author of Kashshaaf Al-Qinaa’ said, "Ghusl is not obligatory in case semen comes out for another reason such as sickness or cold or a broken back from a person who is not asleep, insane, unconscious, drunk. In such a case, no ghusl is required, only ablution..."

In case the emission is pre-seminal fluid, then the person should wash his private parts and the traces of mathy on his clothes if he wants to perform the prayer in those clothes. He is not obliged to perform ablution immediately after the emission of mathy, just as it is not obligatory to perform ablution after urinating except when the person wants to perform prayer. He does not have to perform ablution immediately after the emission of mathy except once he wants to perform the prayer afterwards.

Al-Kashmeeri wrote in his commentary on Sunan At-Tirmithi, “The majority of the scholars held that ablution after the emission of mathy is one of the rulings related to the prayer, so it is obligatory when the person wants to perform prayer.”

Al-Haafith Ibn Hajar commented on the hadeeth narrated on the authority of ʻAli about mathy saying:

“Ghusl is not obligatory immediately upon the emission of mathy, as stated in the version of the hadeeth cited by Abu Daawood and others. Scholars reached a scholarly consensus in this regard. Hence, the command to perform ablution after the emission of mathy is similar to the command of performing ablution in case of relieving oneself as stated above by the compiler ... At-Tahaawi narrated that a group of scholars held that ablution is obligatory upon the emission of mathy. He refuted their view relying on the report narrated on the authority of ʻAbdur-Rahmaan ibn Abi Layla that says that the Messenger of Allaah, sallallaahu ʻalayhi wa sallam, was asked about mathy and said, 'For that, ablution (is necessary), and for maniyy, ghusl is necessary.' It is deduced that the ruling on the emission of mathy is the same as on the emission of urine and similar invalidators of ablution, not that it necessitates immediate ablution...” [Fat-h Al-Baari]

It is possible that the emission is wady, which is a thick white discharge that comes out after urinating or with urine. Wady is impure and necessitates ablution. For more benefit, please refer to fatwa 82518.

Allaah knows best.