Which Surah is called al-Muqashqishah?

Surat At-Tawbah is called "Al-Muqashqishah" (The Cleanser), "Bara'ah" (Immunity), and "Al-Fadihah" (The Discloser), because it cleanses those who believe in it from hypocrisy. This name is also given to Surat Al-Kafirun because it cleanses from polytheism, and to Surahs Al-Falaq and An-Nas. Therefore, the name "Al-Muqashqishah" is shared among Surahs At-Tawbah, Al-Kafirun, Al-Falaq, and An-Nas, with Surat At-Tawbah being the most famous by this name.