It is narrated from Mundhir bin Amr al-Wadi'i that Sayyiduna Umar (may Allah be pleased with him) sent him in command of cavalry in Syria (al-Sham), and among the horses were barathin (non-Arab horses). The (Arab) horses went ahead, and the owners of the barathin (non-Arab horses) came (later). Then Mundhir bin Amr gave two shares to the horse and one share to its owner. Then he wrote to Sayyiduna Umar bin al-Khattab (may Allah be pleased with him), and he said: "You have hit upon the Sunnah."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الفيء والغنيمة / 12881