So ʿUmar ibn al-Khaṭṭāb, may Allah be pleased with him, asked the Prophet ﷺ, “If someone becomes in a state of janābah (major ritual impurity) at the beginning of the night, may he lie down to sleep while still junub?”

The Prophet ﷺ allowed it, on condition that the person first lessen the major impurity by performing a valid wudūʾ (ablution). Once that is done, there is no harm in sleeping while junub.

Points derived from the ḥadīth
1 – It is permissible for a person in janābah to sleep before taking a ghusl (ritual bath) provided he performs ablution first.
2 – The higher standard is not to sleep while junub until one has performed ghusl; relying on ablution alone is merely a concession.
3 – It is recommended for the junub to perform ablution before sleeping if he has not yet bathed.
4 – It is disliked to sleep while junub without either ghusl or ablution.

The ruling on a woman’s nocturnal emission
Umm Salamah, the wife of the Prophet ﷺ, related: “Umm Sulaym, the wife of Abū Ṭalḥah, came to the Messenger of Allah ﷺ and said, ‘Messenger of Allah, Allah is not shy of the truth. Is a woman required to perform ghusl if she experiences a nocturnal emission?’ The Messenger of Allah ﷺ replied, ‘Yes, if she notices the fluid.’”

Overall meaning
Umm Sulaym al-Anṣāriyyah approached the Prophet ﷺ with a delicate question. Because it pertained to intimate matters that people are usually embarrassed to mention, she opened with a preamble to ease the listeners: Allah—the Truth—is not too shy to state the truth when there is benefit in doing so.

After this courteous introduction she asked directly: Is a woman obliged to perform ghusl if, in a dream, she imagines that she is having intercourse? The Prophet ﷺ answered, “Yes, she must perform ghusl if she sees that sexual fluid has been discharged.”

Points derived from the ḥadīth
1 – A woman is required to perform ghusl after a nocturnal emission if she experiences climax and notices the fluid.