وَعَنْهُ، عَنْ اَلنَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «مَنْ أَدْخُلُ فَرَساً بَيْنَ فَرَسَيْنِ (وَهُوَ لَا يَأْمَنُ أَنْ يَسْبِقَ) فَلَا بَأْسَ بِهِ، وَإِنْ أَمِنَ فَهُوَ قِمَارٌ»
“If anyone introduces a horse in a race with two other horses, when he is not certain that it cannot be beaten, there is no harm in it, but when he is certain (it cannot be beaten) it is then considered as gambling.” Related by Ahmad and Abu Dawud with a weak chain of narrators.
Bulugh al-Maram 1510, Book 11, Jihad, Hadith 62. 1 min read