Translation
(56) Fighting for the Cause of Allah (Jihaad)
كتاب الجهاد والسير
(47) Chapter: What has been said about the evil omen of a horse
(47) باب مَا يُذْكَرُ مِنْ شُؤْمِ الْفَرَسِ
Sahih al-Bukhari 2859 

Narrated Sahl bin Sa`d Saidi:

Allah's Messenger (ﷺ) said "If there is any evil omen in anything, then it is in the woman, the horse and the house."

حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ، عَنْ مَالِكٍ، عَنْ أَبِي حَازِمِ بْنِ دِينَارٍ، عَنْ سَهْلِ بْنِ سَعْدٍ السَّاعِدِيِّ ـ رضى الله عنه ـ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ ‏ "‏ إِنْ كَانَ فِي شَىْءٍ فَفِي الْمَرْأَةِ وَالْفَرَسِ وَالْمَسْكَنِ ‏"‏‏.‏
Reference : Sahih al-Bukhari 2859
In-book reference : Book 56, Hadith 75
USC-MSA web (English) reference : Vol. 4, Book 52, Hadith 111
  (deprecated numbering scheme)