None of you should drink while standing, and whoever forgets, then let him induce vomit
Authentic hadithعن أنسٍ رضي الله عنه عن النبيِّ صلى الله عليه وسلم : أَنَّهُ نَهَى أَنْ يَشْرَبَ الرجلُ قَائِمًا. قال قَتَادَةُ: فقلنا لأنسٍ: فالأَكْلُ؟ قال: ذلك أَشَرُّ - أو أَخْبَثُ. وفي رواية: أَنَّ النبيَّ صلى الله عليه وسلم زَجَرَ عن الشُّرْبِ قائمًا. عن أبي هريرة رضي الله عنه مرفوعاً: «لَا يَشْرَبَنَّ أَحَدٌ منكم قَائِمًا، فمن نَسِيَ فَلْيَسْتَقِئْ».
Anas (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) forbade drinking while standing. Qatādah said: "We asked Anas: What about eating? He said: That is even worse - or more detestable." Another narration reads: "The Prophet (may Allah's peace and blessings be upon him) forbade drinking while standing." Abu Hurayrah (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "None of you should drink while standing, and whoever forgets, then let him induce vomit."
Explanation
Anas (may Allah be pleased with him) reported: The Prophet (may Allah's peace and blessings be upon him) forbade drinking while standing. Then Qatādah ibn Di‘āmah As-Sadūsi (may Allah have mercy upon him) said: "We asked Anas (may Allah be pleased with him) about the ruling on eating while standing? Is it forbidden like drinking? Anas replied: 'That is even worse – or more detestable (than drinking while standing).'" The Prophet (may Allah's peace and blessings be upon him) forbade that anyone drinks while he is standing, and if someone forgot and drank while standing, he should empty his stomach. This is only recommended (not obligatory), so he will not bear sin if he does not vomit what he drank, because drinking while standing is disliked, not prohibited.
Source · Muslim with its two versions
From the Hadith Encyclopedia (hadeethenc.com).