It is narrated from Makhlad al-Ghifari that three slaves were present at Badr, and Sayyiduna Umar (may Allah be pleased with him) used to give each man among them three thousand every year.
It is possible that he singled them out for this because of their honour, that is, because of their presence at Badr, and it is also possible that he gave to them after they had been freed.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الفيء والغنيمة / 12979