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. (Using translation from Abū Dāʾūd 2579)   

عَنِ النَّبِيِّ ﷺ قَالَ مَنْ أَدْخَلَ فَرَسًا بَيْنَ فَرَسَيْنِ وَقَدْ أَمِنَ أَنْ يَسْبِقَ فَهُوَ قِمَارٌ وَمَنْ أَدْخَلَ فَرَسًا بَيْنَ فَرَسَيْنِ وَهُوَ لَا يَأْمَنُ أَنْ يَسْبِقَ فَلَيْسَ بِقِمَارٍ  

[Machine] The Messenger of Allah ﷺ said, "Whoever enters a horse between two horses and is not afraid of being left behind, then it is gambling. And whoever enters a horse between two horses and is afraid of being left behind, then it is not gambling." This was specifically mentioned by Sufyan ibn Husayn and Sa'id ibn Bashir from Az-Zuhri, and it was narrated by Abu Dawood in his book of Sunan.  

أَنَّ رَسُولَ اللهِ ﷺ قَالَ مَنْ أَدْخَلَ فَرَسًا بَيْنَ فَرَسَيْنِ وَهُوَ لَا يَخَافُ أَنْ يُسْبَقَ فَهُوَ قِمَارٌ وَمَنْ أَدْخَلَ فَرَسًا بَيْنَ فَرَسَيْنِ وَهُوَ يَخَافُ أَنْ يُسْبَقَ فَلَيْسَ بِقِمَارٍ تَفَرَّدَ بِهِ سُفْيَانُ بْنُ حُسَيْنٍ وَسَعِيدُ بْنُ بَشِيرٍ عَنِ الزُّهْرِيِّ وَقَدْ أَخْرَجَهُمَا أَبُو دَاوُدَ فِي كِتَابِ السُّنَنِ  

[Machine] He heard Sa'id ibn al-Musayyib saying, "There is no harm in betting on horses if a gambler is involved. If he wins, he takes the lead, and if he loses, there is no harm upon him."  

أَنَّهُ سَمِعَ سَعِيدَ بْنَ الْمُسَيِّبِ يَقُولُ لَيْسَ بِرِهَانِ الْخَيْلِ بَأْسٌ إِذَا أُدْخِلَ فِيهَا مُحَلِّلٌ فَإِنْ سَبَقَ أَخَذَ السَّبْقَ وَإِنْ سُبِقَ لَمْ يَكُنْ عَلَيْهِ شَيْءٌ  

[Machine] Regarding the scholars who follow the opinion of the people of Madinah, they used to say that gambling on horses is permissible if it contains equal conditions. If one takes precedence, they will receive compensation, and if they are overtaken, they will not be fined. It is necessary for the compensator to be similar to the horse in terms of speed and strength.  

عَنِ الْفُقَهَاءِ الَّذِينَ يُنْتَهَى إِلَى قَوْلِهِمْ مِنْ أَهْلِ الْمَدِينَةِ كَانُوا يَقُولُونَ الرِّهَانُ فِي الْخَيْلِ جَائِزٌ إِذَا أُدْخِلَ فِيهَا مُحَلِّلٌ إِنْ سَبَقَ أَخَذَ وَإِنْ سُبِقَ لَمْ يَغْرَمْ شَيْئًا وَيَنْبَغِي أَنْ يَكُونَ الْمُحَلِّلُ شَبِيهًا بِالْخَيْلِ فِي النَّجَاءِ وَالْجَوْدَةِ