[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