I saw the Messenger of Allah ﷺ drinking both standing and sitting.
رأيت رسول الله ﷺ يشرب قائما وقاعدا.
Tirmidhi related it in Jami (1883), and in Shamail (209), Abu Dawud (653), Ibn Majah (931), and Ahmad (6660), all of them through Amr bin Shuayb, from his father, from his grandfather Abdullah bin Amr, who said, then he mentioned it. Its isnad is hasan because of Amr bin Shuayb, for his hadith is hasan, and Tirmidhi also graded it hasan.