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]. (JA)
App reference (JA): Book 3, Hadith 42 (JA)
Arabic/English book reference (JA): Book 3, Hadith 769 (JA)