It is narrated from Sayyiduna Sufyan bin Abdullah (may Allah be pleased with him) that Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) sent him as a zakah collector, and he would count the young lambs and kids against the people (in reckoning the zakah). The people said: "You count the young ones against us, yet you do not take any of them?" When he came to Sayyiduna Umar bin al-Khattab (may Allah be pleased with him), he told him about this, and Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) said to him: "Yes, count against them the young one that the shepherd carries, but do not take it. And do not take the fattened animal, nor the one nursing her newborn, nor the pregnant one, nor the male of the flock; rather take a one-year-old and a two-year-old. That is a fair balance between the inferior and the choicest of the wealth."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6365