Harry Truman actually said...
In the case of appointments under subsection 101(a) hereof, exemption hereunder shall not extend to the receipt or payment of salary in connection with the appointee's Government service hereunder from any source other than the private employer of the appointee at the time of his appointment hereunder.
Context
Executive Order 10205—Amending Executive Order No. 10182 Relating to the Appointment of Certain Persons Under the Defense...
01/15/1951