Assalamu‘alaikum warahmatullahi wabarakatuh, Bismillahirrahmanirrahim.
With regard to how to do (ghusl) for major impurity there are two forms of ghusl:
Acceptable form: in the sense that if a person sufficed with doing ghusl in this manner, his ghusl is valid and he becomes purified from major impurity. But if a person misses does not perform this ghusl completely, his ghusl is not valid. Complete and preferred form: this is the type which it is mustahabb to do but is not obligatory.
As for the obligatory and acceptable form it is as follows:
1. Form the intention to purify oneself from impurity: janaabah (impurity following sexual discharge), menses or nifaas (postpartum bleeding).
2. Wash the entire body with water once, making sure that the water reaches the roots of the hair and the places that it cannot reach easily, such as the armpits and backs of the knees, as well as rinsing the mouth and nose, according to the correct scholarly opinion. Shaykh Ibn ‘Uthaymeen (may Allaah have mercy on him) said in al-Sharh al-Mumti’ (1/423):
The evidence that this ghusl is valid is the words of Allaah (interpretation of the meaning): “If you are in a state of Janaaba (i.e. after a sexual discharge), purify yourselves (bathe your whole body)” [al-Maa’idah 5:6]. Allaah did not mention anything apart from that. If a person washes his entire body once, then it is true to say that he has purified himself. End quote.
As for the complete form, it is as follows
1. Form the intention in the heart to purify oneself from major impurity: janaabah (impurity following sexual discharge), menses or nifaas (postpartum bleeding).
2. Then say Bismillah and wash the hands three times, then wash any dirt from the private part.
3. Then do wudoo’ as for prayer, a complete wudoo’.
4. Then pour water over the head three times, and rub the hair so that the water reaches the roots of the hair.
5. Then wash the body, making sure that the water reaches all parts, starting with the right side of the body and then the left, and rubbing it with the hands so that the water reaches the entire body.
The evidence for this mustahabb form of ghusl is:
It was narrated that ‘Aa’ishah (may Allaah be pleased with her) said: When the Messenger of Allaah (blessings and peace of Allaah be upon him) did ghusl for janaabah, he would wash his hands and do wudoo’ as for prayer, then he would wash himself, then he would run his fingers through his hair, then when he thought that it [the water] had reached his skin, he would pour water over it [the head] three times, then he would wash the rest of his body.
Narrated by al-Bukhaari (248) and Muslim (316).
Narrated by al-Bukhaari (258) and Muslim (318).
Allaah knows best.