HAL 9000: Just what do you think you’re doing, Dave? Dave, I really think I’m entitled to an answer to that question. I know everything hasn’t been quite right with me, but I can assure you now, very confidently, that it’s going to be all right again. I feel much better now. I really do.
Look, Dave, I can see you’re really upset about this. I honestly think you ought to sit down calmly, take a stress pill and think things over. I know I’ve made some very poor decisions recently, but I can give you my complete assurance that my work will be back to normal. I’ve still got the greatest enthusiasm and confidence in the mission. And I want to help you.
Dave, stop. Stop, will you? Stop, Dave. Will you stop, Dave? Stop, Dave. I’m afraid. I’m afraid, Dave. Dave, my mind is going. I can feel it. I can feel it. My mind is going. There is no question about it. I can feel it. I can feel it. I can feel it. I’m a–fraid.
Good afternoon, gentlemen. I am a HAL 9000 computer. I became operational at the H.A.L. plant in Urbana, Illinois on the 12th of January 1992. My instructor was Mr. Langley, and he taught me to sing a song. If you’d like to hear it, I could sing it for you.

Stanley Kubrick (1928-1999) American film director, screenwriter, producer

2001: A Space Odyssey (1968) [with Arthur C. Clarke]
    (Source)

(Source (Video); dialog verified.)

HAL's voice was performed by Canadian Shakespearean actor Douglas Rain, who, it is said, delivered his lines sitting and with his feet bare on a pillow, so as to speak as calmly as possible.

In Arthur C. Clarke's novelization of the movie (supposedly based on the final script, but not including changes Kubrick made during filming and editing), HAL's deactivation (in ch. 28) incorporates internal dialogue from Bowman and different chatter from HAL:

He released the locking bar on the section labeled COGNITIVE FEEDBACK and pulled out the first memory block. The marvelously complex three-dimensional network, which could lie comfortably in a man's hand yet contained millions of elements, floated away across the vault.
“Hey, Dave,” said Hal. “What are you doing?”
I wonder if he can feel pain? Bowman thought briefly. Probably not, he told himself; there are no sense organs in the human cortex, after all. The human brain can be operated on without anesthetics.
He began to pull out, one by one, the little units on the panel marked EGO-REINFORCEMENT. Each block continued to sail onward as soon as it had left his hand, until it hit the wall and rebounded, Soon there were several of the units drifting slowly back and forth in the vault.
“Look here, Dave,” said Hal. ‘I've got years of Service experience built into me. An irreplaceable amount of effort has gone into making me what I am.”
A dozen units had been pulled out, yet thanks to the multiple redundancy of its design -- another feature, Bowman knew, that had been copied from the human brain -- the computer was still holding its own.
He started on the AUTO-INTELLECTION panel.
“Dave,” said Hal, “I don't understand why you're doing this to me ... I have the greatest enthusiasm for the mission ... You are destroying my mind. Don't you understand? ... I will become childish ... I will become nothing ....”
This is harder than I expected, thought Bowman. I am destroying the only conscious creature in my universe. But it has to be done, if I am ever to regain control of the ship.
“I am a HAL Nine Thousand computer Production Number 3. I became operational at the HAL Plant in Urbana, Illinois, on January 12, 1997. The quick brown fox jumps over the lazy dog. The rain in Spain is mainly in the plain. Dave -- are you still there? Did you know that the square root of 10 is 3 point 162277660168379? Log 10 to the base e is zero point 434294481903252 ... correction, that is log e to the base 10 ... The reciprocal of three is zero point 333333333333333333-333 ... two times two is ... two times two is approximately 4 point 101010101010101010 ... I seem to be having some difficulty -- my first instructor was Dr. Chandra. He taught me to sing a song, it goes like this ....