Purity: Completeness of Washing in Ghusl
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 373:
If in ghusl any part of the outer area of the body is left unwashed, the ghusl is invalid. However, washing inside the ears, nose, and whatever is considered an inner part of the body is not obligatory.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)