Answered by: Alimah Nasima Umm Hamza
Assalamu Alaikum Wa Rahmatullah
Who gave ghusl to the prophet Muhammad (PBUH)?
بسم الله الرحمن الرحيم
In the name of Allah, the Most Gracious, the Most Merciful.
The Prophet (saw) was washed by Al-‘Abbas, ‘Ali, AlFadl and Qathm — the two sons of Al-‘Abbas, as well as Shaqran — the Messenger’s freed slave, Usamah bin Zaid and Aws bin Khauli. 
Only Allah Knows Best
Written by Alimah Nasima Umm Hamza
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 The Sealed Nectar, Dar-us-Salam Publications, Page 481