The major ablution (ghusl): when and how

Allah said:

If you are in a state of major impurity, then purify yourselves.sura an-Nisa 43

When ghusl is obligatory

• Emission of sperm with desire (janaba), including in a dream (Muslim 316).
• Penetration even without ejaculation: "When the two circumcised parts meet, ghusl becomes obligatory" (at-Tirmidhi 108).
• The end of menstruation and post-natal bleeding.
• Death: the funeral ghusl, a communal obligation.

The complete manner

From the hadith of Maymuna (al-Bukhari 249):

1. Wash the palms.
2. Wash the private parts.
3. Perform wudu as for prayer.
4. Take water and pour it over the head three times.
5. Wash the whole body.
6. Step aside and wash the foot.

The sufficient manner (the valid minimum for the majority): the intention, passing water over the entire body, including the roots of the hair.

Practical points and differences

• Braided hair: in janaba, water reaches it; for post-natal bleeding, the woman may wipe without undoing them (Muslim 330).
• Order and continuity: a sunnah for the majority, obligatory for some.
• The Friday and Eid ghusls: recommended, not obligatory (majority view).

If water is harmful or unavailable, tayammum replaces it according to its rules.