Zadhan says that once Syedna Ali (may Allah be pleased with him) drank water while standing, and people began to look at him with astonishment. He said: Why are you staring at me? If I have drunk water standing, it is because I saw the Prophet (peace and blessings be upon him) do so, and if I have drunk sitting, I have seen him do that as well.
Hadith Referenceمسند احمد / مسند الخلفاء الراشدين / 1128