Sahih Muslim Book 9, Hadith Number 3501.

Chapter: Mere giving of option of divorce to women does not make divorce effective, but when it is really intended.

Masruq reported: I do not mind if I give option to my wife (to get divorce) once, hundred times, or thousand times after (knowing it) that she has chosen me (and would never seek divorce). I asked ‘Aisha (Allah be pleased with her) (about it) and she said: Allah’s Messenger (may peace be upon him) gave us the option, but did it imply divorce? (It was in fact not a divorce; it is effective when women actually avail themselves of it.)