Musnad Ahmad 482:162

Muhammad ibn Bakr narrated to us, he said: Ibn Jurayj said: Abu Ayyub traveled to Uqbah ibn Amir in Egypt and said: "I am asking you about a matter, of which no one remains who witnessed it with the Messenger of Allah, may Allah bless him and grant him peace, except for me and you. How did you hear the Messenger of Allah, may Allah bless him and grant him peace, speak regarding the covering of a believer?" He said: "I heard the Messenger of Allah, may Allah bless him and grant him peace, say: 'Whoever covers a believer in this world regarding a fault, Allah will cover him on the Day of Resurrection.'" He then returned to Medina, and he did not even unpack his luggage before narrating this hadith.