1. Amr ibn Shu’aib radiyallahu anhu relates from his father, and he from his (Amr’s) grandfather, that he said, I had seen Rasoolullah sallallahu alaihe wasallam drinking water whilst standing and also whilst sitting.
There are many narrations mentioned wherein Sayyidina Rasoolullah sallallahu alaihe wasallam prohibited the drinking of water whilst standing. A narration of Sayyidina Abu Hurairah radiyallahu anhu is mentioned in Sahih Muslim that Sayyidina Rasoolullah sallallahu alaihe wasallam said, No person should stand and drink water, and if one forgetfully stood and drank it, it should be vomited out. Some ulama have summed both the deed and the prohibition in a few ways. Some ulama are of the opinion that the prohibition came later and repeals the previous law. Some ulama hold the opposite view that the narrations where he stood and drank water repeals the one that prohibits it. According to a well-known saying, the prohibition is not that of a Shar’ee or unlawful nature, but as an etiquette. It is also a blessing and kindness. Ibn Qayyim and others have mentioned the harm that standing and drinking causes. In short, Sayyidina Rasoolullah sallallahu alaihe wasallam standing and drinking shows it being permissible to do so, and that it is not haraam to stand and drink water. It is best not do so, as this is against the recommended practice and one will be committing a makrooh act by doing so.
2. Ibn Abbas radiyallahu anhu says, Rasoolullah sallallahu alaihe wasallam drank Zam-zam water while he was standing.
Sayyidina Rasoolullah sallallahu alaihe wasallam has prohibited the drinking of water whilst standing. For this reason some ulama have prohibited the drinking of Zam-zam also whilst standing. They say that he drank it whilst standing because of the huge crowds and the rush, or as a concession. The well-known view of the ulama is that Zam-zam is not included in this prohibition. It is better to stand and drink it.
3. Sayyidina Anas ibn Malik radiyallahu anhu relates that Rasoolullah sallallahu alaihe wasallam drank water in three breaths (i.e. in three gulps/sips) and used to say, It is more pleasing and satisfying in this manner.
It has been prohibited to drink water in one gulp. The Ulama have written many harmful effects in drinking water in one breath. It especially weakens the muscles and nerves. It is also detrimental for the liver and stomach.
4. Sayyidina Ibn Abbas radiyallahu anhu says, Whenever Rasoolullah sallallahu alaihe wasallam drank water, he drank it in two breaths.
In this hadith drinking water in two breaths is intended which apparently seems correct. Sayyidina Ibn Abbas radiyallahu anhu has stated in a hadith of the Prophet sallallahu alaihe wasallam, Do not drink water only in one breath, but drink it in two or three breaths. The minimum number of sips one can take is mentioned in this hadith. Sayyidina Rasoolullah sallallahu alaihe wasallam at times drank water in two sips to show that this was the minimum amount of gulps one could take. Another explanation may be this that in the hadith it meant that two breaths should be taken whilst drinking water. If two breaths are taken whilst drinking water, then all the water will naturally be drunk in three gulps. By this explanation there remains no contradiction between this and the last hadith.