Source, in full
Answer when he was asked why he had not yet reformed the U.N. an its agencies after five months, given that God had taken only seven days to create the universe. As quoted in TIME Magazine (1997), edited by Briton Hadden, Henry Robinson Luce. Time Inc. Volume 149. Issues 2-8. p. 24. Also found in George Antwi (2012), "The Words of Power", Booksmango, p. 103.
Variants
said by Kofi Annan himself during the "Desmond Tutu Annual International Peace Lecture":"Mr. ambassador, you are right. But God had the unique advantage: He worked alone." (He explains that the question was made by the Russian Ambassador of the U.N. at that time).