Amr ibn Shu'aib (may Allah be pleased with him) relates from his father, and he from his (Amr's) grandfather, that he said, I had seen Messenger of Allah ﷺ drinking water whilst standing and also whilst sitting.

حَدَّثَنَا قُتَيْبَةُ بْنُ سَعِيدٍ، قَالَ: حَدَّثَنَا مُحَمَّدُ بْنُ جَعْفَرٍ، عَنْ حُسَيْنٍ الْمُعَلِّمِ، عَنْ عَمْرِو بْنِ شُعَيْبٍ، عَنْ أَبِيهِ، عَنْ جَدِّهِ، قَالَ: رَأَيْتُ رَسُولَ اللهِ ﷺ، يَشْرَبُ قَائِمًا، وَقَاعِدًا.