Today we give our thanks, most of all, for the ideals of honor and faith we inherit from our forefathers — for the decency of purpose, steadfastness of resolve and strength of will, for the courage and the humility, which they possessed and which we must seek every day to emulate. As we express our gratitude, we must never forget that the highest appreciation is not to utter words but to live by them.

John F. Kennedy (1917-1963) US President (1961-63)

Thanksgiving Day Proclamation (4 Nov 1963)
    (Source)

The 1963 Proclamation was written, finalized, and distributed prior to Kennedy's assassination, six days before Thanksgiving.