Jami` at-Tirmidhi 1883
جامع الترمذي#1883Hasanحَدَّثَنَا قُتَيْبَةُ، حَدَّثَنَا مُحَمَّدُ بْنُ جَعْفَرٍ، عَنْ حُسَيْنٍ الْمُعَلِّمِ، عَنْ عَمْرِو بْنِ شُعَيْبٍ، عَنْ أَبِيهِ، عَنْ جَدِّهِ، قَالَ رَأَيْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَشْرَبُ قَائِمًا وَقَاعِدًا . قَالَ أَبُو عِيسَى هَذَا حَدِيثٌ حَسَنٌ صَحِيحٌ .
Narrated 'Amr bin Shu'aib: From his father, from his grandfather who said: "I saw the Messenger of Allah (ﷺ) drinking while standing and sitting." [Abu 'Eisa said:] This Hadith is Hasan Sahih
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
Ahmad Muhammad ShakirHasan
Al-AlbaniHasan
Bashar Awad MaaroufHasan
Zubair Ali ZaiIsnaad Hasan
In-book reference: 26:23