The Kitzur Shulchan Aruch in 42:2 states that - "One shouldn't eat while standing and not drink while standing."
Now as I understand, the Kitzur (written by Rabbi Shlomo Ganzfried) is a summary of the Shulchan Aruch, which in turn is largely based on the Beit Yosef, which is a commentary on the Arba'ah Turim.
Is this prohibition mentioned in the Shulchan Aruch, Beit Yosef, Tur or any other work? Or did Rabbi Ganzfried add it based on his own knowledge?
This is a related question which was asked on Mi Yodeya, however it does not mention the verse in the Kitzur. Forbidden to eat while standing up?