Sahih Bukhari
Medicine
Volume: 007 / Book Number: 071 / Hadith Number: 650
Narrated Abu Huraira:
I heard Allah's Apostle saying, "There is no Tiyara, and the best omen is the Fal." They asked, "What is the Fal?" He said, "A good word that one of you hears (and takes as a good omen)."