Sayyiduna Abu Hurayrah (may Allah be pleased with him) said that the Prophet (peace and blessings be upon him) forbade "drinking by putting one's mouth to the mouth of a water-skin." Ayyub (may Allah have mercy on him) said: I was told that a man drank by putting his mouth to the mouth of a water-skin, and a snake came out of it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأشربة والحد فيها / 17492