"But if you do not—and you will never be able to—then fear the Fire, whose fuel is men and stones," which are stones of sulfur.

Muhammad said: "Waquduha" (its fuel), with a fatha on the waw, refers to its firewood. "Al-wuqud" (the process of igniting), with a damma, is the verbal noun (masdar); it is said: "Waqadat al-naru taqudu wuqudan" (the fire ignited, it ignites, an ignition).