Muwatta Malik #1049
Jihad
The Arabic includes the chain of narration (sanad) and the collector's commentary; the English translation shows the Prophet's words only.
وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ يَحْيَى بْنِ سَعِيدٍ، أَنَّهُ سَمِعَ سَعِيدَ بْنَ الْمُسَيَّبِ، يَقُولُ لَيْسَ بِرِهَانِ الْخَيْلِ بَأْسٌ إِذَا دَخَلَ فِيهَا مُحَلِّلٌ فَإِنْ سَبَقَ أَخَذَ السَّبَقَ وَإِنْ سُبِقَ لَمْ يَكُنْ عَلَيْهِ شَىْءٌ .
Yahya related to me from Malik that Yahya ibn Said heard Said ibn
al-Musayyab say, "There is no harm in placing stakes on horses if a
third horse enters it. The winner takes the stake, and there is no
fine against the loser."
About Muwatta Malik
This hadith is #1049 from Muwatta Malik, in the Book of Jihad.