From Sahih Bukhari (Hadith 5754):
Narrated Abu Huraira:I heard Allah's Messenger (ﷺ) 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)
Reference: Bukhari 5754