Sahih Bukhari Volume 7, Book 74, Hadith 5618

حَدَّثَنَا آدَمُ، حَدَّثَنَا شُعْبَةُ، حَدَّثَنَا عَبْدُ الْمَلِكِ بْنُ مَيْسَرَةَ، سَمِعْتُ النَّزَّالَ بْنَ سَبْرَةَ، يُحَدِّثُ عَنْ عَلِيٍّ ـ رضى الله عنه ـ أَنَّهُ صَلَّى الظُّهْرَ ثُمَّ قَعَدَ فِي حَوَائِجِ النَّاسِ فِي رَحَبَةِ الْكُوفَةِ حَتَّى حَضَرَتْ صَلاَةُ الْعَصْرِ، ثُمَّ أُتِيَ بِمَاءٍ فَشَرِبَ وَغَسَلَ وَجْهَهُ وَيَدَيْهِ وَذَكَرَ رَأْسَهُ وَرِجْلَيْهِ، ثُمَّ قَامَ فَشَرِبَ فَضْلَهُ وَهْوَ قَائِمٌ ثُمَّ قَالَ إِنَّ نَاسًا يَكْرَهُونَ الشُّرْبَ قَائِمًا وَإِنَّ النَّبِيَّ صلى الله عليه وسلم صَنَعَ مِثْلَ مَا صَنَعْتُ‏

Narrated By An-Nazzal bin Sabra : 'Ali offered the Zuhr prayer and then sat down in the wide courtyard (of the Mosque) of Kufa in order to deal with the affairs of the people till the 'Asr prayer became due. Then water was brought to him and he drank of it, washed his face, hands, head and feet. Then he stood up and drank the remaining water while he was standing. and said, "Some people dislike to drink water while standing thought the Prophet did as I have just done."