As I heard it told, the concept that the units are inseparably part of the quantity can be traced back to (who else?) Leonard Euler. My problem is, Euler was so

As I heard it told, the concept that the units are inseparably part of the quantity can be traced back to (who else?) Leonard Euler. My problem is, Euler was so stupendously prolific that he effectively Google-bombed his own name, so trying to dig up my original source has proved futile. :-[