Musannaf Ibn Abi Shayba 9:1046

Ibn ‘Uyaynah narrated to us, from Malik, from Abu Qilabah, from Anas, who said: "When a man marries a virgin [while he is already] married, he stays with her for seven [days], and when he marries a previously married woman, he stays with her for three [days]." Khalid said: Abu Qilabah said, "If I were to say that he attributed it to the Prophet, I would be truthful, but he [only] said: 'The Sunnah is such.'" Khalid said: I narrated it to Ibn Sirin, and he said: "You have added to it; this is four, and this is a night."