Muwatta Malik 1106

وَحَدَّثَنِي عَنْ مَالِكٍ، عَنْ حُمَيْدٍ الطَّوِيلِ، عَنْ أَنَسِ بْنِ مَالِكٍ، أَنَّهُ كَانَ يَقُولُ لِلْبِكْرِ سَبْعٌ وَلِلثَّيِّبِ ثَلاَثٌ ‏.‏

Yahya related to me from Malik from Humayd at-Tawil that Anas ibn Malik said, "A virgin has seven nights, and a woman who has been previously married has three nights." Malik affirmed, "That is what is done among us." Malik added, "If the man has another wife, he divides his time equally between them after the wedding nights. He does not count the wedding nights against the one he has just married

Reference

Muwatta Malik 1106

In-book

Book 28, Hadith 16