Yasar bin Numayr said that Sayyiduna Umar (may Allah be pleased with him) said: I swear that I will not give certain people anything, but later I give to them. When you see that I have done this, then on my behalf feed ten poor persons, giving every two poor persons one sa' of wheat or one sa' of dates.
This was the view of Sayyiduna Umar (may Allah be pleased with him). Perhaps he considered more to be recommended, or perhaps less than this also suffices.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19978