´It was narrated that Sulaiman bin Yasar said:` "I entered upon Umm Salamah and she told me that the Messenger of Allah (ﷺ) used to wake up in a state of Janabah without having had a wet dream, then he would fast." And she told him that she brought the Prophet (ﷺ) some grilled ribs and he ate from that, then he got up and prayed, and did not perform Wudu'.
Hadith Referenceسنن نسائي / صفة الوضوء / 183
Hadith Gradingالألبانی:صحيح | زبیر علی زئی:صحيح مسلم
Hadith Takhrij«تفرد بہ النسائی، (تحفة الأشراف: 18160)، وقد أخرجہ: صحیح مسلم/الصوم 13 (1109)، مسند احمد 6/306 (صحیح)»
➊ Janabah (major ritual impurity) can occur at any time due to a wet dream (ihtilam) or sexual intercourse (jima‘), therefore the Shari‘ah has provided leeway that if someone finds themselves in this situation and wishes to fast, but does not have time for a ritual bath (ghusl)—if they perform the bath, they will miss the pre-dawn meal (suhoor)—then it is permissible for them to begin the fast in this state and perform the bath later before the prayer. If someone experiences a wet dream during the fast, it does not affect the validity of the fast.
➋ The apparent meaning of «لم یمس ماء» can also be intended. That is, it is not absolute, because rinsing the mouth (madmadah) is not obligatory, and it is possible that this is a figurative expression for not performing ablution (wudu); this is the clear point.
Source: Sunan Nasa'i: Translation and Benefits by Shaykh Hafiz Muhammad Amin Hafizullah, Page: 183