Hadith 761
Abu Sa'id Al-Khudri (May Allah be pleased with him) reported:
عن أبى سعيد الخدرى رضى الله عنه قال : نهى رسول الله عن اختناث الأسقية : يعنى: أن تكسر أفواهها، ويشرب منها.((متفق عليه))
The Messenger of Allah (ﷺ) forbade turning the water-skin upside down and drinking directly from its mouth. [Al-Bukhari and Muslim].
In plain words
He forbade turning a water-skin upside down to drink from its mouth. Pouring into a cup first is the cleaner, more careful way.
Reference : Riyad as-Salihin 761 In-book reference : Book 2, Hadith 35