رِيَاضُ الصَّالِحِينَ
Riyad as-Salihin 766
The Book About the Etiquette of Eating
Permission to Drink While Standing
وَعَنِ ابْنِ عَبَّاسٍ رضى اللَّهُ عَنْهُمَا قَالَ: سَقَيْتُ النَّبِيَّ صَلَّى اللَّه عَلَيْهِ وَسَلَّمَ مِنْ زَمْزَمَ، فَشَرِبَ وَهُوَ قَائِمٌ .((مُتَّفَقٌ عَلَيْهِ))
Ibn 'Abbas (May Allah be pleased with them) reported: I served the Messenger of Allah (ﷺ) Zamzam water to drink and he drank it while he was standing. [Al-Bukhari and Muslim].
Riyad as-Salihin, 766