Jami` at-Tirmidhi Book 47, Hadith 385
The Messenger of Allah said: “Whoever wishes to look at the Day of Resurrection, as if he is seeing it with this eye, then let him recite: ‘When the sun Kuwwirat’ and ‘When the heaven is cleft sunder (Infatarat) and ‘When the heaven is split asunder.’”
the Prophet said: “You will be gathered barefoot, naked and uncircumcised.” “A woman said: “Will we see” or “look at each other’s nakedness?” He said: “O so-and-so! Every man among them on that Day will have enough to make him careless of others.”
the Messenger of Allah said: “Verily, when the slave (of Allah) commits a sin, a black spot appears on his heart. When he refrains from it, seeks forgiveness and repents, his heart is polished clean. But if he returns, it increases until it covers his entire heart. And that is the ‘Ran’ which Allah mentioned: ‘Nay, but on their hearts is the Ran which they used to earn.’”