Umm ad-Darda' said, "Abu'd-Darda' stood up in the night to pray.He was weeping and said, 'O Allah! You made my physical form good, so makemy character good!' until morning. I said, 'Abu'd-Darda', your only supplicationfor the entire night was for good character!' He replied, 'Umm ad-Darda',the Muslim makes his character good with the result that his good charactertakes him into the Garden. He makes his character bad with the result thathis bad character takes him into the Fire. The Muslim is forgiven whilehe is asleep.' I asked, 'Abu'd-Darda', how can be forgiven while he isasleep?' He said, 'His brother arises in the night and performs the nightprayers and makes supplication to Allah Almighty and is answered. He makessupplication for Muslim brother and his request is answered.'"
English reference: Book 14, Hadith 290
Arabic reference: Book 1, Hadith 290