What was the secret message that the Prophet (PBUH) confided in one his wives?

66:3 with tafseer . There are different interpretation of it, some interpretation deals with Maria, other with Abu Bakar, Umar and then some regarding Ali (RA). What is the correct interpretation of this verse? > And when the prophet secretly communicated a piece of information to > one of his wives-- but when she informed (others) of it, and Allah > made him to know it, he made known part of it and avoided part; so > when he informed her of it, she said: Who informed you of this? He > said: The Knowing, the one Aware, informed me. Do we have any authentic evidence regarding the secret message? Also what is not clear, was it Aisha (RA) or Hafsa (RA) to whom this secret was revealed.