Musnad Ahmad 30:129

Sufyan narrated to us, from al-Zuhri, from Sa’id, from Abu Hurayrah, from the Prophet, may God bless him and grant him peace, who said: "The Fire complained to its Lord, saying: 'My parts are consuming one another.' So He permitted it two breaths: one breath in the winter and one breath in the summer. Therefore, the most intense heat you experience is from the scorching heat of Hell."