The Messenger of Allah ﷺ forbade drinking directly from the mouth of a waterskin.
حدثنا يونس حدثنا حماد يعني ابن زيد عن أيوب عن عكرمة
أن رسول الله ﷺ نهى عن الشرب من فم السقاء
Abu Dawud, Tirmidhi, and Ibn Majah narrated it from Ibn Abbas, and Suyuti indicated its soundness in Jami Saghir. He also reported it in this wording, "He forbade drinking from the mouth of a waterskin," and in this wording, "He forbade drinking from the mouth of a waterskin, and riding an animal that eats filth, and eating an animal left tethered to be killed." The last one was narrated by Abu Dawud, Tirmidhi, Nasai, and Hakim, who likewise indicated its soundness.