Quoted in Time, 31 July 1973. Usually attributed to Robinson, but slightly earlier evidence is found in the Guthrian (Guthrie County, Iowa), 26 Jan. 1970, which printed "Close only counts in horse shoes and grenades."
George R. R. Martin (2012). “George R. R. Martin's A Game of Thrones 5-Book Boxed Set (Song of Ice and Fire Series): A Game of Thrones, A Clash of Kings, A Storm of Swords, A Feast for Crows, and and A Dance with Dragons”, p.187, Bantam