The Book Pertaining to Repentance and Exhortation to Repentance (Kitab Al-Tauba)
Muslim :: Book 37 : Hadith 6636
'Ala' reported on the authority of his father who reported on the authority of Abu Huraira that Allah's Messenger (may peace be upon him) said: If a believer were to know the punishment (in Hell) none would have the audacity to aspire for Paradise (but he would earnestly desire to be rescued from Hell), and if a non-believer were to know what is there with Allah as a mercy. none would have been disappointed in regard to Paradise.