The Prophet ﷺ said: If one enters a horse with two others when he is not certain that it cannot be beaten, it is not gambling; but when one enters a horse with two others when he is certain it cannot be beaten, it is gambling.  

عَنِ النَّبِيِّ ﷺ قَالَ مَنْ أَدْخَلَ فَرَسًا بَيْنَ فَرَسَيْنِ يَعْنِي وَهُوَ لاَ يُؤْمَنُ أَنْ يُسْبَقَ فَلَيْسَ بِقِمَارٍ وَمَنْ أَدْخَلَ فَرَسًا بَيْنَ فَرَسَيْنِ وَقَدْ أَمِنَ أَنْ يُسْبَقَ فَهُوَ قِمَارٌ  

The tradition mentioned above has also been transmitted by Al Zuhri with the chain of ‘Abbad and to the same affect. Abu Dawud said “This tradition has also been narrated by Ma’mar, Shu’aib and ‘Aqil on the authority of Al Zuhri from a number of scholars and this is the soundest one in our opinion.