Abd al-Rahman bin Uthman (may Allah be pleased with him) said: I was with Sayyiduna Umar (may Allah be pleased with him) on a journey to Makkah when a riding party of Thaqif gave him two water-skins of nabidh. He drank one of them. Then milk was given to him as a gift, so he drank the milk and left the nabidh. Then, after some time, he came to drink the nabidh and saw that it had become thick, so he said: "Break it with water." Its thickening was, and Allah knows best, due to sourness or sweetness. Likewise it is reported from Nafi' (may Allah have mercy on him) that Sayyiduna Umar (may Allah be pleased with him) said to Yarfa': Go to our brothers and look for a drink for us with them. He went to them, and they said: We have nothing but this water-flask, and it has changed. Sayyiduna Umar (may Allah be pleased with him) called for it, tasted it and frowned; then he called for water, poured it over it and drank. Nafi' (may Allah have mercy on him) said: By Allah, he only frowned because it had turned to vinegar.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأشربة والحد فيها / 17449