Firstly: Defining Ritual Washing
Ghusl linguistically: is pouring water over a thing.
Ghusl technically: is pouring water over the whole body with an appropriate intention.
Secondly: Defining Janabah
Janabah linguistically: is furtherance.
Janabah technically: is ejaculation or the insertion of the male private part into the female’s. This name is used as it legally keeps a person ‘far’ from prayer.
Thirdly: What Necessitates Washing and What Does Not Ejaculating when awake with arousal
If a person ejaculates when awake with arousal then washing is wajib for them. This is the position of the majority: Hanafis,  Al-Sarkhasi said: “That which is considered by Abu Hanifah and Muhammad – Allah have mercy upon them – is semen exiting with force and arousal, whereas what is considered by Abu Yusuf – Allah have mercy upon him – is semen being visible.” Al-Mabsut (120/1). Abu Yusuf from the Hanafis as well as the Hanbalis required it as a condition for washing that semen exits as an ejaculatory – i.e. with force and in spurts – to conform to His statement, exalted: “[Man is] created from spurted fluid.” [al-Tariq:6]. Others viewed that arousal suffices as a condition in the stead of ejaculation with force, as ejaculation does not take place except with arousal. Malikis, and Hanbalis. The rest of semen exiting after washing
If there was remaining semen and it exited after washing then there is no need for washing and ablution suffices. This is the position of the Malikis, the common position among Hanbalis, a group from the Salaf, and the choice of Ibn Taymiyyah, Ibn Baz, and Ibn `Uthaymin. Nocturnal emission
If a person has a dream where they are aroused and they subsequently ejaculate, they must wash for purification. Consensus has been quoted over this by: Ibn Hazm, Ibn `Abd al-Barr, Ibn Qudamah, al-Nawawi, and Ibn Taymiyyah. Whoever sees a sexual dream but does not ejaculate
If a person sees a dream where they are aroused but they do not ejaculate, or they do not see any evidence of ejaculating upon waking, then they do not have to wash. This is by agreement of the four schools of jurisprudence. Whoever sees semen but does not recall dreaming
If a person wakes to find semen but does not remember having a sexual dream, then he must wash for purification. This is by agreement of the four schools of jurisprudence. Whoever sees moisture but doubts it being semen or pre-seminal fluid
If a person sees moisture upon waking but is unsure of it being semen or pre-seminal fluid, then he does not have to wash. This is the most common opinion among Shafi`is, the position of Abu Yusuf, a position among Malikis, a position among Hanbalis, the position of a group of the Salaf. Al-Baghawi mentions it as being the position of the majority of scholars, and it is also the choice of Ibn al-Mundhir, Ibn Qudamah, Ibn Baz, and Ibn `Uthaymin. Vaginal intercourse
Washing is an obligation after vaginal intercourse by consensus, even if ejaculation does not take place. This is by agreement of the four schools of jurisprudence, and the majority of scholars hold this position. Private parts touching
If the penis comes in contact with the vagina without penetration or ejaculation, then washing is not an obligation for either. Consensus is quoted on this by: Ibn al-`Arabi, Ibn Qudamah, al-Nawawi, and al-Shawkani. Anal intercourse, male or female
Anal intercourse necessitates washing, regardless if it’s a man or a woman. This is by agreement of the four schools of jurisprudence. Immediate washing from janabah
It is not necessary to perform ritual washing immediately after becoming junub. Consensus is quoted over this by al-Nawawi and Siraj al-Deen al-Hindi. Ending of menstruation or postnatal bleeding
It is wajib to wash after menstruation or postnatal bleeding has ended. Consensus has been quoted over this by: al-Tabari, bn al-Mundhir, Ibn Hazm, al-Kasani, Ibn Qudamah, and al-Nawawi. Multiple reasons for washing
If there is more than one reason for washing, then one wash suffices, and this is by agreement of the four schools of jurisprudence.