The Messenger of Allah (صلي الله عليه وسلم) said: “My entire nation is safe, except al-Mujahirin (those who boast of their sins). Among the Mujaharah is that a man commits an (evil) act, and wakes up in the morning while Allah has kept his (sin) a secret, he says: “O so-and-so! Last night I did this and that.” He goes to sleep while Allah has kept his (sin) a secret but he wakes up in the morning and uncovers what Allah has kept a secret!” [Saheeh al-Bukhari]

Abdullah Ibn Masoud (رضي الله عنه) related, ‘A man came to the Prophet and said: ‘O Messenger of Allah! I have mingled with a woman in the far side of al-Medina, and I fulfilled my desire short of actually having sexual intercourse with her. So, here am I, judge me according to what you decide.’ Umar Ibn al-Khattab (رضي الله عنه) then said: ‘Allah had kept your secret, why did not you keep your secret?’ [Sharh Muslim] Similarly, if one becomes aware of somebody else’s sin, he should keep it a secret. Allah’s Messenger (صلي الله عليه وسلم) said: “He, who relieves a hardship of this Dunya (world) for a believer, Allah will relieve (from him) a hardship of the Day of Resurrection; he who makes easy an indebted person, Allah will make it easy for him in the Dunya and the Hereafter; he who covers a Muslim (meaning his mistakes and shortcomings), Allah will cover him in the Dunya and the Hereafter …” [Muslim]

http://www.ilmfruits.com/do-not-reveal-your-sins