It is narrated from Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) that the Prophet Muhammad (peace and blessings be upon him) forbade drinking directly from the mouth of a water-skin.
Hadith Referenceالسنن المأثورة / باب الحدود / 548
Hadith Takhrijصحیح مسلم، الاشربة، باب آداب الطعام والشراب وأحكامهما، رقم: 2023۔