Language:
كتاب النكاح
67  
Wedlock, Marriage (Nikaah)
(101)
Chapter: Marrying a virgin while already having a matron wife
(100)
باب إِذَا تَزَوَّجَ الْبِكْرَ عَلَى الثَّيِّبِ
Sahih al-Bukhari 5213

Narrated Anas:

The tradition, (of the Prophet) is that if someone marries a virgin and he has already a matron wife (with him), then he should stay with the virgin for seven days; and if someone marries a matron (and he has already a virgin wife with him) then he should stay with her for three days.

حَدَّثَنَا مُسَدَّدٌ، حَدَّثَنَا بِشْرٌ، حَدَّثَنَا خَالِدٌ، عَنْ أَبِي قِلاَبَةَ، عَنْ أَنَسٍ ـ رضى الله عنه ـ وَلَوْ شِئْتُ أَنْ أَقُولَ قَالَ النَّبِيُّ صلى الله عليه وسلم وَلَكِنْ قَالَ السُّنَّةُ إِذَا تَزَوَّجَ الْبِكْرَ أَقَامَ عِنْدَهَا سَبْعًا، وَإِذَا تَزَوَّجَ الثَّيِّبَ أَقَامَ عِنْدَهَا ثَلاَثًا‏.‏
Reference : Sahih al-Bukhari 5213
In-book reference : Book 67, Hadith 146
USC-MSA web (English) reference : Vol. 7, Book 62, Hadith 140
  (deprecated numbering scheme)