It is narrated from Sayyidah Aishah (may Allah be pleased with her) that she said: "The Messenger of Allah (peace and blessings be upon him) would eat both standing and sitting (in both states)."
Imam al-Harith bin Abi Usamah narrated this hadith in his Musnad. Its chain is da'if (weak), because it contains Yahya bin Hashim, who is matruk (one whose narrations were abandoned), and Ibn Abi Layla also had a weak memory; however, the permissibility of eating and drinking while standing is established by other sahih and reliable hadith.
Hadith Referenceالمطالب العالية بزوائد المسانيد الثمانية / كتاب الأطعمة والأشربة / 2404
Hadith Gradingمحدثین:إسناده موضوع
Hadith Takhrij«حکم الحدیث المطالب العالیہ محققاً تنسیق د. سعد بن ناصر بن عبد العزيز الشَّثري- مکتبہ شاملہ :حديث موضوع. » «أخرجه مسند أحمد برقم: 7337، وأخرجه مجمع الزوائد ومنبع الفوائد برقم: 2241»