وعن ابن عمر رضى الله عنهما
قال: كنا نأكل على عهد رسول الله صلى الله عليه وسلم ونحن نمشى، ونشرب ونحن قيام
During the lifetime of the Messenger of Allah (sallallahu alayhi wa sallam) we would eat while walking and would drink while standing.
Riyad as-Salihin 768, Book 3, The Book About the Etiquette of Eating, Hadith 42. 1 min read