The Messenger of Allah ﷺ forbade drinking directly from the mouth of a waterskin.Ayub said, "I was told that a man drank from the mouth of a waterskin and a snake came out of it."
حدثنا إسماعيل قال أخبرنا أيوب عن عكرمة
أن رسول الله ﷺ نهى أن يشرب من في السقاء قال أيوب أنبئت أن رجلا شرب من في السقاء فخرجت حية
Its isnad is sahih. Bukhari related it, 10/90 no. 5627, in the Book of Drinks, chapter on drinking from the mouth of a waterskin. Also Muslim, 2/1600 no. 2023, Abu Dawud, 3/336 no. 3719, Ibn Majah, 2/1132 no. 3420, and Darimi, 2/140 no. 2118.