Purity: The Intention in Wudu
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 281:
It is not necessary for one to actually utter the intention (niyyah) of performing wuḍūʾ or feel it in his heart; rather, it is sufficient if he performs all the acts of wuḍūʾ in compliance with the command of Allah the Exalted.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)