The Book of Drinks
وَحَدَّثَنَاهُ عَبْدُ بْنُ حُمَيْدٍ، أَخْبَرَنَا عَبْدُ الرَّزَّاقِ، أَخْبَرَنَا مَعْمَرٌ، عَنِ الزُّهْرِيِّ، بِهَذَا الإِسْنَادِ . مِثْلَهُ غَيْرَ أَنَّهُ قَالَ وَاخْتِنَاثُهَا أَنْ يُقْلَبَ رَأْسُهَا ثُمَّ يُشْرَبَ مِنْهُ .This hadith has been reported from Zuhri with the same chain of transmitters, but he also said that Ikhtinath means that its head (i. e., of the waterskin) be turned upside down and then (water) be drank from that
From Sahih Muslim, whose reports the scholars accept as authentic.