Sahih Muslim Book 009, Hadith Number 3499.
Chapter: Mere giving of option of divorce to women does not make divorce effective, but when it is really intended.
'Aisha (Allah be pleased with her) reported that Allah's Messenger (may peace be upon him) sought our permission when he had a (turn to spend) a day with (one of his wives) amongst us (whereas he wanted to visit his other wives too). It was after this that this verse was revealed: "Thou mayest put off whom thou pleasest of them, and take for thee whom thou pleasest" (xxxiii. 5). Mu'adha said to her: What did you say to Allah's Messenger (may peace be upon him) when he sought your permission? She said: I used to say: If it had the option in this I would not have (allowed anyone) to have precedence over me.