Ghusl is washing the whole body with water. It is mandatory for one to have a Ghusl in the following instances:
1. Discharge of seminal fluid as a result of sexual excitement, whether he is awake or asleep (i.e. a wet dream). The Prophet (peace and blessing be upon him) said:
"When the seminal fluid is discharged (as a result of sexual excitement) have a Ghusl.' (Abu Dawood).
2. Sexual intercourse. Once the private parts touch, one must have a Ghusl even without ejaculation. The Prophet (peace and blessing be upon him) said:
"Once the two private parts come into contact, Ghusl becomes mandatory.' (Ahmed)
3. At the end of a menstrual period. The Prophet (peace and blessing be upon him) said:
(Therefore keep away from women during menses and go not unto them till they have purified (from menses and have taken a bath). And when they have purified themselves, then go in unto them as Allah has ordained for you (go in unto them in any manner as long as it is in their vagina).) (2:222)
4. At the end of a post-natal period.
5. When a non-Muslim embraces Islam.
6. When a Muslim dies, it is mandatory that he be given a Ghusl and be prepared for burial.
It is commendable to have a Ghusl in the following instances:
1. Before attending the Friday prayer. The Prophet (peace and blessing be upon him) said:
"It is a (compulsory) right upon every Muslim that he bathes once every seven days. He should wash his head and his body.' (Bukhari).
2. Before attending the two Eid prayers.
3. After having washed a dead body. The Prophet (peace and blessing be upon him) said:
"Whoever washes the body of a dead person let him have a Ghusl and whoever carries the dead let him make Wudhu.' (Ahmed).
4. Before entering Makkah. Imam Ibn al-Mundhir said: "It is praiseworthy to have Ghusl before entering Makkah, according to all the Scholars. No offering must be offered if one leaves this aside. Majority of the Scholars mentioned that performing Wudhu is sufficient."
Pillars of Ghusl
1. Niyyah (intention) that is the intention to perform Ghusl.
One should not utter the intention. Uttering the intention is an act of Bid'ah (innovation) which should be forsaken.
2. Water must reach all parts of the body. Allah says:
(If you are in a state of Janaba (i.e. had a sexual discharge), purify yourself (bathe your whole body).) (5:6).
3. Making sure that water reaches the roots of the hair.
Sunnah acts of Ghusl
1. Tasmiyyah, i.e. to say 'Bismillah'.
2. Washing the hands three times before commencing the Ghusl.
3. Washing the private region and removing any defilement.