ず[に] ... (attendant circumstances, means)
Usage
Vないform ~~ない~~ + ず[に]... Indicates attendant circumstances or means. It is the same as ないで but is more in the written than in the spoken style.
Examples
その男は先週の土曜日にこの店に来て、一言も話さず、酒を飲んでいた。
That guy came to this bar last Saturday and was drinking without saying a word.