Who said "he who is in a rush shall walk slowly"? A while back I read the saying "he who is in a rush shall walk slowly". I have seen it be attributed to Confucius (https://www.wer-weiss-was.de/t/redewendung-wer-es-eilig-hat-soll-langsam-gehen/8457422 https://www.quotez.net/german/konfuzius.htm) sometimes, but never in any academic reference.

Who is the author of the sentence and where was it written down first?
"he who is in a rush shall walk slowly” was translation of a Japanese proberbs,  and many of them came from Chinese literatures 

The idiom 欲速則不達 (If you rush you are more likely not getting there)  came from 論語 and the writer was 子路.