Purity: Doubt About Wudu After Prayers

Practical Laws of Islam as per the teachings of Ayatullah Sistani

Ruling 303:

If a person doubts after prayers whether he had performed wuḍūʾ or not, his prayers are valid but he must perform wuḍūʾ for subsequent prayers.

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