A man dies when he refuses to stand up for that which is right. A man dies when he refuses to stand up for justice. A man dies when he refuses to take a stand for that which is true.

Martin Luther King, Jr. (1929-1968) American clergyman, civil rights leader, social activist, preacher

Sermon, Selma, Alabama (8 Mar 1965)

Possibly the source of the uncited attributions (or variants) "Our lives begin to end the day we become silent about things that matter" and "The day we see the truth and cease to speak is the day we begin to die."