Sahih Bukhari Volume 005, Book 058, Hadith Number 182.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 58. Merits of the Helpers in Madina (Ansaar)
Narated By 'Aisha : Abu Bakr had a slave who used to give him some of his earnings. Abu Bakr used to eat from it. One day he brought something and Abu Bakr ate from it. The slave said to him, "Do you know what this is?" Abu Bakr then enquired, "What is it?" The slave said, "Once, in the pre-Islamic period of ignorance I foretold somebody's future though I did not know this knowledge of foretelling but I, cheated him, and when he met me, he gave me something for that service, and that is what you have eaten from." Then Abu Bakr put his hand in his mouth and vomited whatever was present in his stomach.