1- Emission of Semen

It is a thick white liquid which exits in spurts due to sexual stimulation and is followed by a loss of strength. Its scent resembles that of a rotten egg. The need for a ghusl is stated in Allah’s saying: “If you are in a state of janaba (ritual impurity), purify yourself (bathe your whole body).”(Al-Ma’idah:6)
And the Prophet’s ﷺ saying: “When you ejaculate, take a ghusl.” [ narrated by Abu Dawud.]
Points for Discussion
1- If a person has a wet dream yet doesn’t ejaculate, he does not have to make ghusl.
2- If he wakes up and doesn’t remember having a wet dream, yet he finds semen on himself, clothes, bed, etc. he must take a ghusl. The Prophet ﷺ said, “Water is only from water.” [ narrated by Muslim.] In other words the emission of semen - willfully or unwillfully - necessitates a ghusl.
3- If he feels semen moving in his penis, yet it does not exit, he does not have to make a ghusl.
4- If it exits due to some sort of sickness and not from sexual stimulation, then he does not have to take a ghusl.
5- If his state necessitated a ghusl, and he took a ghusl, but then semen exited immediately after the ghusl, he is not obliged to take another ghusl. He only has to make wudu’.
6- When a person wakes up from sleep and notices wetness on his clothes whose cause he can’t remember, then the following three conditions are possible:
a) He is sure that the wetness is semen. Then, it is obligatory on him to take a bath, whether he remembers having a wet dream or not.
b) He is sure it is not semen. In this case there is no need to take a bath. The ruling thus will be that of urine (i.e. wudu’).
c) He doubts whether it is semen or not, he must then examine the situation and recall what took place. If it occurs to him that it is semen, then it is semen. However, if it occurs to him that it was something else, then he considers it to be something else. But if nothing occurs to him, then it is compulsory (on him) to take a bath so that he can avoid any error.
7-If he sees semen on himself, but cannot remember when it was produced, it is compulsory to take a bath and repeat the Salah (prayer) from the last time he slept.
2. Sexual Intercourse

It is the meeting of the male and the female sexual organs. This is by the insertion of the head of the male’s penis into the female’s vagina. This is sexual intercourse even if ejaculation doesn’t occur. The Prophet ﷺ said: “When the circumcised penetrates the circumcised, bathing is compulsory.” [ narrated by At-Tirmidhi.]
3. When a non-believer becomes a Muslim

This is because “the Prophet ﷺ ordered Qais Ibn ‘Asim t to take a bath when he became a muslim.” [ narrated by Abu Dawud.]
4. At The End of a Menstrual Cycle or Post-natal Bleeding

This is in accordance with the hadeeth related by A’ishah (may Allah be pleased him), when the Prophet ﷺ told Fatimah bint Abi Hubaysh: “When menstruation starts (you should) stop praying, and when it leaves, take a (purificatory) bath, then start praying again.” [ agreed upon.] It’s the consensus of the scholars of Islam that post-natal bleeding is like menstruation.
5. Death

This is according to the statement of the Prophet ﷺ when he told those preparing Zaynab (his daughter) for burial: “Wash her three times, five times or more if you think (it is necessary).” [ agreed upon.]