What does it mean?
The poet's love is so natural and deep that he can't explain when it started or where it comes from.
Who said it?
Pablo Neruda: Chilean poet (1904–1973). Source: One Hundred Love Sonnets, XVII (1959).
Love– Pablo Neruda, One Hundred Love Sonnets, XVII (1959)
“I love you without knowing how, or when, or from where.”