Richard Nixon actually said...
Now, Therefore, I, Richard M. Nixon, President of the United States of America, in accordance with the wish of the Congress as expressed in Section 6103 of Title 5 of the United States Code, do hereby proclaim Thursday, November 22, 1973, as a day of national thanksgiving, and concurrently, a day of prayer for the memory of John F. Kennedy.
Context
Proclamation 4255—Thanksgiving Day, 1973
11/15/1973