Sahih Muslim Book 37, Hadith Number 6636.

Chapter : The mercy of Allah predominates his wrath.

‘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.