Here is a link to hear his entire Mountaintop speech from Memphis TN -- April 3, 1968. The conclusion is excerpted below:
And they were telling me, now it doesn't matter now. It really doesn't
matter what happens now. I left Atlanta this morning, and as we got
started on the plane, there were six of us, the pilot said over the
public address system, "We are sorry for the delay, but we have Dr.
Martin Luther King on the plane. And to be sure that all of the bags
were checked, and to be sure that nothing would be wrong with the plane,
we had to check out everything carefully. And we've had the plane
protected and guarded all night."
And then I got to Memphis. And some began to say the threats, or talk
about the threats that were out. What would happen to me from some of
our sick white brothers?
Well, I don't know what will happen now. We've got some difficult days
ahead. But it doesn't matter with me now. Because I've been to the
mountaintop. And I don't mind. Like anybody, I would like to live a long
life. Longevity has its place. But I'm not concerned about that now. I
just want to do God's will. And He's allowed me to go up to the
mountain. And I've looked over. And I've seen the promised land. I may
not get there with you. But I want you to know tonight, that we, as a
people, will get to the promised land. And I'm happy, tonight. I'm not
worried about anything. I'm not fearing any man. Mine eyes have seen the
glory of the coming of the Lord.