6:120Al-An'aam

All the people of my Ummah would get pardon for their sins except those who publicise them. And (it means) that a servant should do a deed during the night and tell the people in the morning that he has done so and so, whereas Allah has concealed it. And he does a deed during the day and when it is night he tells the people, whereas Allah has concealed it. Zuhair has used the word hijar for publicising.

“Whoever covers (the sin of) a Muslim, Allah will cover him (his sin) in this world and in the Hereafter.”

I heard Allah's Messenger (ﷺ) saying. "All the sins of my followers will be forgiven except those of the Mujahirin (those who commit a sin openly or disclose their sins to the people). An example of such disclosure is that a person commits a sin at night and though Allah screens it from the public, then he comes in the morning, and says, 'O so-and-so, I did such-and-such (evil) deed yesterday,' though he spent his night screened by his Lord (none knowing about his sin) and in the morning he removes Allah's screen from himself."

The Prophet (ﷺ) said: When sin is done in the earth, he who sees it and disapproves of it will be taken like one who was not present, but he who is not present and approves of it will be like him who sees.

“When the believer commits sin, a black spot appears on his heart. If he repents and gives up that sin and seeks forgiveness, his heart will be polished. But if (the sin) increases, (the black spot) increases. That is the Ran that Allah mentions in His Book: “Nay! But on their hearts is the Ran (covering of sins and evil deeds) which they used to earn.”