Sahih Bukhari Volume 008, Book 078, Hadith Number 654.

Narated By Anas bin Malik : The Prophet said, "The Hell Fire will keep on saying: 'Are there anymore (people to come)?' Till the Lord of Power and Honor will put His Foot over it and then it will say, 'Qat! Qat! (sufficient! sufficient!) by Your Power and Honor. And its various sides will come close to each other (i.e., it will contract)."