What is qunut al-nawazil?

If a calamity befalls the Muslims, it is permissible for them to perform Qunut in the last rak'ah of all prescribed prayers, either before or after bowing (ruku'). This is what the Prophet, peace and blessings be upon him, did. He performed Qunut for a month, supplicating against certain Arab tribes. He performed Qunut in the Maghrib and Fajr prayers, and he also performed Qunut in the Dhuhr, Asr, Maghrib, Isha, and Subh prayers. The jurists have differed on this Qunut, holding four different opinions. The correct view according to the Hanbali school is that Qunut is performed in all prescribed prayers except Friday prayer. They also differed regarding Qunut for a plague. The Hanbalis held that Qunut is not performed to ward off a plague, while the Hanafis and Shafi'is held that it is recommended to perform Qunut to avert a plague.