When the Messenger of Allah ﷺ married Umm Salamah, he stayed with her three night, and said: Your people (i.e. clan) are not being humbled for you in my estimation. If you wish I shall stay with you seven nights; and if I stay with you seven nights, I shall stay with my other wives seven nights.  

أَنَّ رَسُولَ اللَّهِ ﷺ لَمَّا تَزَوَّجَ أُمَّ سَلَمَةَ أَقَامَ عِنْدَهَا ثَلاَثًا ثُمَّ قَالَ لَيْسَ بِكِ عَلَى أَهْلِكِ هَوَانٌ إِنْ شِئْتِ سَبَّعْتُ لَكِ وَإِنْ سَبَّعْتُ لَكِ سَبَّعْتُ لِنِسَائِي  

When the Messenger of Allah ﷺ married Safiyyah, he stayed with her three nights. The narrator 'Uthman added: She was non virgin (previously married). He said: This tradition has been narrated to me by Hushaim, reported by Humaid, and transmitted by Anas.  

لَمَّا أَخَذَ رَسُولُ اللَّهِ ﷺ صَفِيَّةَ أَقَامَ عِنْدَهَا ثَلاَثًا زَادَ عُثْمَانُ وَكَانَتْ ثَيِّبًا وَقَالَ حَدَّثَنِي هُشَيْمٌ أَخْبَرَنَا حُمَيْدٌ أَخْبَرَنَا أَنَسٌ  

When a man who has a wife married a virgin he should stay with her seven nights ; if he marries to a woman who has been previously married he should stay with her three nights. (The narrator said:) If I say that he (Anas) narrated this tradition from the Prophet ﷺ I shall be true. But he said: The Sunnah is so-and-so.  

إِذَا تَزَوَّجَ الْبِكْرَ عَلَى الثَّيِّبِ أَقَامَ عِنْدَهَا سَبْعًا وَإِذَا تَزَوَّجَ الثَّيِّبَ أَقَامَ عِنْدَهَا ثَلاَثًا وَلَوْ قُلْتُ إِنَّهُ رَفَعَهُ لَصَدَقْتُ وَلَكِنَّهُ قَالَ السُّنَّةُ كَذَلِكَ