Source, in full
First words upon returning to Earth, to a woman and a girl near where his capsule landed (12 April 1961) The woman asked: "Can it be that you have come from outer space?" to which Gagarin replied: "As a matter of fact, I have!"
Notes from Wikiquote
Quoted in The Air Up There : More Great Quotations on Flight (2003) by Dave English, p. 118