Attributed to Kahlil Gibran
«"If you love somebody, let them go, for if they return, they were always yours. And if they don't, they never were."»
Misattributed
Verdict
It is not in Kahlil Gibran's work
It circulates widely under Gibran's name, but it does not appear in The Prophet, The Madman, The Forerunner or Sand and Foam (checked against Project Gutenberg and Wikisource), nor in the anthologies of his Arabic work. It is an anonymous self-help maxim from the second half of the twentieth century.
What they did say
Verified words of Kahlil Gibran
«Your children are not your children. They are the sons and daughters of Life’s longing for itself.»
The Prophet (1923), «On Children»
«You are the bows from which your children as living arrows are sent forth.»
The Prophet (1923), «On Children»
«Work is love made visible.»
The Prophet (1923), «On Work»