Sahih Muslim Book 40, Hadith Number 6816.
Chapter : The description of hell and the intensity of its heat and torments.
Samura b. Jundub reported Allah’s Messenger (may peace be upon him) as saying: There would be among them those to whom the fire will reach up to their ankles and to some of them the fire would reach their knees and to some it would reach their waists and to some it would reach up to their collar-bones.