From the BBC:

A curfew has been imposed in Bauchi in northern Nigerian after at least 13 people were killed in a sectarian riot. It began as an argument between a teacher and a pupil over the confiscation of a Koran in school.

But rumours swept the city that the book had been desecrated and that was the cue for youths, some armed with machetes, to rampage in the streets.

From the caption accompanying a photo in a Washington Post piece on rioters in Afghanistan:

"Ataullah Najafi, ... in Herat, in West Afghanistan, shows the remains of hundreds of Korans burned by Sunni rioters who descended on the mosque on Feb. 9.