Purity: Intention for Ghusl
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 357:
It is not necessary that at the time of performing ghusl one make the intention of performing an obligatory ghusl; rather, it is sufficient if one performs ghusl with only the intention of qurbah, i.e. in humility to the Lord of the worlds.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)