Abu Huraira reported: The Prophet, peace and blessings be upon him, said, “A servant does not cover the faults of another servant but that Allah will cover his faults on the Day of Resurrection.”

Source: Sahih Muslim 2590

Grade: Sahih (authentic) according to Muslim

عَنْ أَبِي هُرَيْرَةَ عَنْ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ لَا يَسْتُرُ عَبْدٌ عَبْدًا فِي الدُّنْيَا إِلَّا سَتَرَهُ اللَّهُ يَوْمَ الْقِيَامَةِ

2590 صحيح مسلم كِتَاب الْبِرِّ وَالصِّلَةِ وَالْآدَابِ لا يستر الله على عبد في الدنيا إلا ستره الله يوم القيامة

http://dailyhadith.abuaminaelias.com/2014/05/19/hadith-on-faults-allah-will-cover-the-faults-of-those-who-cover-the-faults-of-others/