Purity: Validity of Wudu When Duty is Tayammum

Practical Laws of Islam as per the teachings of Ayatullah Sistani

Ruling 280:

If due to the shortage of time for prayers one’s duty is to perform tayammum, but instead he performs wuḍūʾ with the intention of attaining proximity to Allah (qaṣd al‑qurbah), or [he performs wuḍūʾ] for a recommended act like reciting the Qur’an, then the wuḍūʾ he performed is valid [despite the fact that his duty was to perform tayammum]. Similarly, the wuḍūʾ would still be valid if he performed it with the intention of performing that prayer unless he did so without the intention of attaining proximity to Allah the Exalted.

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