O Abu Turab!

In a narration of Sahih Bukhari, Hazrat Sohail (ra) bin Saad relates that the Holy Prophet (sa) went to the house of Hazrat Fatimah (ra), but did not find Hazrat Ali (ra) at home. The Holy Prophet (sa) enquired, “Where is the son of your paternal uncle?” Hazrat Fatimah (ra) replied, “We had an argument. He was upset with me and left and did not take his siesta at home either.” Upon this, the Holy Prophet (sa) instructed someone to look for him. This individual returned and said, “O Messenger (sa) of Allah! He is sleeping in the mosque.” The Holy Prophet (sa) went to the mosque and found Hazrat Ali (ra) lying there. His back was slightly uncovered as a result of which it had some dust on it. The Holy Prophet (sa) wiped away the dust and said, “Get up, O Abu Turab! Get up, O Abu Turab!” Since then, he started being called by the title of Abu Turab [the Father Dust].

(Sahih al-Bukhari, Kitab al-Salah, Bab Naum al-Rijal fi al-Masjid, Hadith 441)