“Nonsense,” Weston denied, with an involuntary nervous shiver. “That’s completely ridiculous. We had a long discussion at the time we bought Robbie about the First Law of Robotics. You know that it is impossible for a robot to harm a human being; that long before enough can go wrong to alter that First Law, a robot would be completely inoperable. It’s a mathematical impossibility. Besides I have an engineer from U. S. Robots here twice a year to give the poor gadget a complete overhaul. Why, there’s no more chance of anything at all going wrong with Robbie than there is of you or I suddenly going looney—considerably less, in fact. Besides, how are you going to take him away from Gloria?”

"Runaround" in Astounding Science Fiction (March 1942); later published in I, Robot (1950)
The Three Laws of Robotics (1942)

“Evidence”, p. 151
I, Robot (1950)

Source: One Day

"Runaround" in Astounding Science Fiction (March 1942); later published in I, Robot (1950)
The Three Laws of Robotics (1942)
Variant: A robot may not injure a human being, or, through inaction, allow a human being to come to harm.

Excerpt from the book The Goodbye Family Unveiled (2017) by Lorin Morgan-Richards.

Yours, Isaac Asimov (20 September 1973) <!-- page 329 -->
General sources
Context: What I will be remembered for are the Foundation Trilogy and the Three Laws of Robotics. What I want to be remembered for is no one book, or no dozen books. Any single thing I have written can be paralleled or even surpassed by something someone else has done. However, my total corpus for quantity, quality and variety can be duplicated by no one else. That is what I want to be remembered for.

R.U.R. (1920)

The Transhumanism Handbook, 2019