It is narrated from Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) "forbade drinking water from the mouths of waterskins."
Al-Asma'i said: "Ikhtinath" means folding back the mouth of the waterskin and drinking from it, or turning the mouth of the waterskin upward and drinking from it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصداق / 14661
Sayyiduna Abu Sa'id al-Khudri (may Allah be pleased with him) narrates that a man drank from the mouth of a waterskin and a small snake slipped into his stomach, so the Messenger of Allah (peace and blessings be upon him) forbade folding back the mouths of waterskins and drinking from them.
Isma'il al-Makki has some weakness.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصداق / 14662
Sayyiduna Abu Hurayrah (may Allah be pleased with him) said: I will inform you of some things from the Messenger of Allah (peace and blessings be upon him): "None of you should drink water by putting his mouth to the mouth of a waterskin."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصداق / 14663
وَأَخْبَرَنَا أَبُو عَبْدِ اللهِ الْحَافِظُ، نا أَبُو بَكْرِ بْنُ إِسْحَاقَ، أنا بِشْرُ بْنُ مُوسَى، نا الْحُمَيْدِيُّ، نا سُفْيَانُ، نا أَيُّوبُ السَّخْتِيَانِيُّ، نا عِكْرِمَةُ قَالَ: أَلَا أُخْبِرُكُمْ بِأَشْيَاءَ قِصَارٍ سَمِعْنَاهَا مِنْ أَبِي هُرَيْرَةَ؟ قَالَ: نَهَى رَسُولُ اللهِ صَلَّى اللهُ عَلَيْهِ وَسَلَّمَ أَنْ يُشْرَبَ مِنْ فَمِ السِّقَاءِ " رَوَاهُ الْبُخَارِيُّ فِي الصَّحِيحِ، عَنْ عَلِيِّ بْنِ عَبْدِ اللهِ عَنْ سُفْيَانَ.
Ikrimah (may Allah have mercy on him) said: Shall I not inform you of some short things that I heard from Abu Hurayrah (may Allah be pleased with him)? That the Messenger of Allah (peace and blessings be upon him) "forbade drinking by putting one's mouth to the mouth of a waterskin."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصداق / 14664
Ayyub (may Allah have mercy on him), through his chain, narrates from the Prophet (peace and blessings be upon him) that he (peace and blessings be upon him) "forbade a man to drink from the mouth of a waterskin (by putting his mouth to it)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصداق / 14665
Hisham bin Urwah (may Allah have mercy on him) narrates from his father that the Prophet (peace and blessings be upon him) forbade drinking from the mouth of a waterskin and said: "It becomes spoiled." It has been narrated like this as mursal. As for what has been narrated granting permission in this matter, the reports of prohibition are more authentic in their chains.
Some scholars have interpreted it (the permission) as applying when the waterskin is hanging, so that the creatures of the earth cannot get into it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصداق / 14666