كتـــــاب أدب الطعام
3
The Book About the Etiquette of Eating
Ibn 'Umar (May Allah be pleased with them) reported:
During the lifetime of Messenger of Allah (ﷺ) we would eat while walking and would drink while standing.

[At- Tirmidhi].

وعن ابن عمر رضى الله عنهما قال‏:‏كنا نأكل على عهد رسول الله صلى الله عليه وسلم ونحن نمشى ، ونشرب ونحن قيام‏.‏ ‏.‏
Sunnah.com reference : Book 3, Hadith 42
Arabic/English book reference : Book 3, Hadith 769