Sahih Bukhari Volume 008, Book 073, Hadith Number 161.
Narated By Abu Juhaifa : The Prophet established a bond of brotherhood between Salman and Abu Darda'. Salman paid a visit to Abu ad-Darda and found Um Ad-Darda' dressed in shabby clothes and asked her why she was in that state.?" She replied, "Your brother, Abu Ad-Darda is not interested in the luxuries of this world." In the meantime Abu Ad-Darda came and prepared a meal for him (Salman), and said to him, "(Please) eat for I am fasting." Salman said, "I am not going to eat, unless you eat." So Abu Ad-Darda' ate. When it was night, Abu Ad-Darda' got up (for the night prayer). Salman said (to him), "Sleep," and he slept. Again Abu-Ad-Darda' got up (for the prayer), and Salman said (to him), "Sleep." When it was the last part of the night, Salman said to him, "Get up now (for the prayer)." So both of them offered their prayers and Salman said to Abu Ad-Darda',"Your Lord has a right on you; and your soul has a right on you; and your family has a right on you; so you should give the rights of all those who have a right on you). Later on Abu Ad-Darda' visited the Prophet and mentioned that to him. The Prophet, said, "Salman has spoken the truth."