It is narrated from Zayd bin Aslam (may Allah have mercy on him) that Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) drank some milk, and it amazed him. He asked the one who had given it to him to drink: Where did you get this milk from? He told him that he had gone to a watering place, and he named that watering place, and there were sadaqah goats there which they were watering. They milked some of their milk for me, and I put it in this vessel of mine. Sayyiduna Umar (may Allah be pleased with him) put his finger (into his mouth) and vomited it out.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الصدقات / 13164
Sulayman bin Yasar (may Allah have mercy on him) says that Ibn Abi Rabi'ah came with the charity wealth over which he was the collector. When he reached the place called al-Harrah, Sayyiduna Umar bin al-Khattab (may Allah be pleased with him) came out to him there; he (Ibn Abi Rabi'ah) set dates, milk and butter before him. The others ate, but Sayyiduna Umar (may Allah be pleased with him) refused to eat. Ibn Abi Rabi'ah said: "By Allah, may Allah set you right, we drink their milk and benefit from them." He said: "O Ibn Abi Rabi'ah! I am not like you; by Allah, you follow behind their tails." (That is, you look after them.)
Hadith Referenceالسنن الكبرى للبيهقي / كتاب قسم الصدقات / 13165