Mishkat al-Masabih 13 Marriage كتاب النكاح 151

وَعَنْ أَبِي قِلَابَةَ عَنْ أَنَسٍ قَالَ: مِنَ السُّنَّةِ إِذَا تَزَوَّجَ الرَّجُلُ الْبِكْرَ عَلَى الثَّيِّبِ أَقَامَ عِنْدهَا سبعا وَقسم إِذا تَزَوَّجَ الثَّيِّبَ أَقَامَ عِنْدَهَا ثَلَاثًا ثُمَّ قَسَمَ. قَالَ أَبُو قلَابَة: وَلَو شِئْت لَقلت: إِن أَنَسًا رَفْعَهُ إِلَى النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ

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.)