عن ابن عباس قال نهى رسول الله صلى الله عليه وسلم عن الشرب من في السقاء (مشكوة المصابيح رقم 4264)
Hadhrat ibn Abbaas (Radhiallahu Anhuma) reports that Rasulullah (Sallallahu Alaihi Wasallam) stopped us from drinking directly from the mouth of a water bag (as its contents could not be seen).
2. It is Mustahab for one to drink while sitting. However if it is Zam Zam water or the remaining water in the utensil after wudhu, then one may stand and drink the water.
عن ابن عباس : أن النبي صلى الله عليه و سلم شرب من زمزم وهو قائم (ترمذي رقم 1882)
Hadhrat ibn Abbaas (Radhiallahu Anhuma) reports that Rasulullah (Sallallahu Alaihi Wasallam) drank Zam Zam water while he was standing.
عن أبي حية قال : رأيت عليا توضأ فغسل كفيه حتى أنقاهما ثم مضمض ثلاثا واستنشق ثلاثا وغسل وجهه ثلاثا وذراعيه ثلاثا ومسح برأسه مرة ثم غسل قدميه إلى الكعبين ثم قام فأخذ فضل طهوره فشربه وهو قائم ثم قال أحببت أن أريكم كيف كان طهور رسول الله صلى الله عليه و سلم (ترمذي رقم 48)
Hadhrat Abu Hayya (Rahmatullahi Alaihi) reports that I had once seen Hadhrat Ali (Radhiallahu Anhu) perform wudhu (in the following manner). He commenced by washing his hands till his wrists until he thoroughly cleansed them, thereafter he gargled his mouth thrice and inserted water in his nose thrice. Thereafter he washed his face thrice, and washed his hands till his elbows thrice. He thereafter made masah of the head once and washed his feet till the ankles. Subsequently, he took the water that was remaining in the utensil and whilst standing he drank the water. Addressing the people he said: “It was my desire to show you the wudhu of Rasulullah (Sallallahu Alaihi Wasallam) (i.e. this was how he performed his wudhu).”