It’s from The Hitch Hiker’s Guide to the Galaxy.
In The Hitchhiker’s Guide to the Galaxy (published in 1979), the
characters visit the legendary planet Magrathea, home to the
now-collapsed planet-building industry, and meet Slartibartfast, a
planetary coastline designer who was responsible for the fjords of
Norway. Through archival recordings, he relates the story of a race of
hyper-intelligent pan-dimensional beings who built a computer named
Deep Thought to calculate the Answer to the Ultimate Question of Life,
the Universe, and Everything. When the answer was revealed to be 42,
Deep Thought explained that the answer was incomprehensible because
the beings didn’t know what they were asking. It went on to predict
that another computer, more powerful than itself would be made and
designed by it to calculate the question for the answer. (Later on,
referencing this, Adams would create the 42 Puzzle, a puzzle which
could be approached in multiple ways, all yielding the answer 42.)