Tirmidhi

Urdu Footnote:
Note:

(In the chain of narration, Abu Muslim Jazmi is acceptable when supported by corroborating narrations; otherwise, he is considered weak in hadith, i.e., a weak narrator. However, by being strengthened through Hadith number 1879, this hadith also becomes sahih li-ghayrihi [authentic due to supporting evidence].)

Benefits and Issues:

➊
In Sahih Muslim, there are narrations from Anas, Abu Sa'id al-Khudri, and Abu Hurairah radi Allahu anhum from the Prophet sallallahu alayhi wa sallam, which establish the prohibition of drinking water while standing. In fact, Abu Sa'id al-Khudri used the word "zajr," meaning he scolded or strictly forbade it.
And Abu Hurairah narrated this statement of the Prophet:
Whoever forgets (and drinks water while standing),
then he should vomit it out.

➋
Hafiz Ibn Hajar rahimahullah, after mentioning the hadiths of prohibition and permissibility, and after mentioning the various opinions and evidences of the scholars, gave preference to the view that drinking while standing is makruh tanzihi (discouraged but not sinful). See:
(Fath al-Bari: 10/103, 106)
And Allah knows best.

➌
Eating while standing is more disliked than drinking while standing.

➍
Eating while walking is an occasional matter, about which there is no doubt regarding its permissibility, but nowadays, the permissibility of eating while standing at gatherings is questionable, because in this:

Firstly, it is a crude imitation of non-Muslims.

Secondly, it is the way of animals and cattle, which is not befitting for humans.

Thirdly, it is also contrary to human dignity.

Fourthly, the chaos that ensues from this method leads to a great deal of food wastage; therefore, this method at gatherings is impermissible and contains numerous objectionable aspects.
And Allah knows best.