Mishkat al-Masabih 19 Jihad كتاب الجهاد 199

وَعَنِ ابْنِ عُمَرَ: أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَسْهَمَ لِلرَّجُلِ وَلِفَرَسِهِ ثَلَاثَةَ أَسْهُمٍ: سَهْمًا لَهُ وَسَهْمَيْنِ لِفَرَسِهِ

Ibn ‘Umar told that God’s Messenger allotted three portions for a man and his horse, one for him and two for his horse. (Bukhari and Muslim.)