“Liner notes, Music Bank box set, 1999.”

Google It: Total Information Awareness, 2016

As quoted in Turning Numbers into Knowledge: Mastering the Art of Problem Solving (2001) by Jonathan G. Koomey, p. 96; since at least 2010 similar statements are also sometimes attributed to Mozart, and a similar remark, apparently one of Ben Jonson, is quoted in "Notes to Cynthia's Revels, in The Works of Ben Jonson: With Notes Critical and Explanatory, and a Biographical Memoir (1875), edited by William Gifford, Vol. 2, in notes to p. 223, on p. 551: Division, in music, is "the space between the notes of music, or the dividing of the tones."
Unsourced variants:
Music is the silence between the notes.
The music is not in the notes, but in the silence between.
The music is not in the notes, but in the silence between them.
Variant: Music is the space between the notes.

Letter to Thomas Cooper, 1814. ME 14:61
Posthumous publications, On financial matters

Remember When the Music
Song lyrics, Sequel (1981)

Awakening : Conversations with the Masters (2003), p. 24
Context: The genius of a composer is found in the notes of his music; but analyzing the notes will not reveal his genius. The poet's greatness is contained in his words; yet the study of his words will not disclose his inspiration. God reveals himself in creation; but scrutinize creation as minutely as you wish, you will not find God, any more than you will find the soul through careful examination of your body.

The Dignity of Human Nature (1754)

Source: The Name of the Wind