Sahih Muslim Book 45, Hadith 93
The servant (who conceals) the faults of others in this world, Allah would conceal his faults on the Day of Resurrection.
The servant (whose fault) Allah conceals in this world, Allah would also conceal (his faults) on the Day of Resurrection.
Grant him permission. (and also added: ) He is a bad son of his tribe or he is a bad person of his tribe. When he came in he used kind words for him. 'A'isha reported that she said: Allah's Messenger, you said about him what you had to say and then you treated him with kindness. He said: A'isha, verily in the eye of Allah, worst amongst the person in rank on the Day of Resurrection is one whom the people abandon or desert out of the fear of indecency.