Sahih Bukhari
Medicine
Volume: 007 / Book Number: 071 / Hadith Number: 651
Narrated Abu Huraira:
The Prophet said, "There is no Tiyara and the best omen is the Fal," Somebody said, "What is the Fal, O Allah's Apostle?" He said, "A good word that one of you hears (and takes as a good omen)."