Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said: I saw the Messenger of Allah (peace and blessings be upon him) drinking Zamzam while standing. In the narration of Shadhan: I gave the Prophet (peace and blessings be upon him) Zamzam water to drink, and he (peace and blessings be upon him) drank it while standing.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصداق / 14646