Purity: Correcting Sequence Errors in Ghusl

Practical Laws of Islam as per the teachings of Ayatullah Sistani

Ruling 361:

In case one washes his body before his head and neck, it is not necessary for him to repeat the ghusl; rather, in the event that one rewashes his body, his ghusl will be valid.

-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)