From Sahih Bukhari (Hadith 3331):
Narrated Abu Huraira:Allah's Apostle said, "Treat women nicely, for a woman is created from a rib, and the most curved portion of the rib is its upper portion, so, if you should try to straighten it, it will break, but if you leave it as it is, it will remain crooked. So treat women nicely
Reference: Bukhari 3331