Abu Qilaba quoted Anas as saying

It pertains to the sunna that when a man who has a wife marries a virgin he should stay with her for seven nights and then divide the time between them, but if he marries a woman who has been previously married he should stay with her three nights and then divide his time between his wives. Abu (Qilaba remarked that if he wished he could say that Anas traced it to the Prophet. (Bukhari and Muslim.)