بُلُوغُ الْمَرَامِ
Bulugh al-Maram 1057
Marriage
وَعَنْ أَنَسٍ قَالَ : { مِنَ اَلسُّنَّةِ إِذَا تَزَوَّجَ اَلرَّجُلُ اَلْبِكْرَ عَلَى اَلثَّيِّبِ أَقَامَ عِنْدَهَا سَبْعًا , ثُمَّ قَسَمَ , وَإِذَا تَزَوَّجَ اَلثَّيِّبَ أَقَامَ عِنْدَهَا ثَلَاثًا , ثُمَّ قَسَمَ } مُتَّفَقٌ عَلَيْهِ , وَاللَّفْظُ لِلْبُخَارِيّ ِ [1] .
Narrated Anas (RA): It is from the Sunnah that when a man who has a wife marries a virgin, he should spend with her seven nights, and thereafter divide time between them (equally). And if he marries a formerly married woman he should spend with her three nights and thereafter divide the time between his wives (equally). [Agreed upon: the wording is al-Bukhari's].
Sunnah.com reference: Book 8, Hadith 106