Jesus Himself says "as Jonas was three days and three nights in the whale's belly; so shall the Son of man be three days and three nights in the heart of the earth" (Mat 12:40) and Paul says "Now that he ascended, what is it but that he also descended first into the lower parts of the earth?" (Eph 4:9) By "lower parts of the earth" and "heart of the earth" is clearly not meant the sepulchre which by no means could go down so deep to warrant such descriptions, but rather hades to which his soul descended is meant.