Abu Qilabah (may Allah have mercy on him) said that Sayyiduna Anas bin Malik (may Allah be pleased with him) said: "The Sunnah is that when a man marries a virgin while having a previously married wife, he should stay with her seven days; and when he marries a previously married woman while having a virgin wife, he should stay with her three days." Khalid (may Allah have mercy on him) said: If I were to say that he narrated this hadith as marfu' (from the Prophet), that too would be true.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب القسم والنشوز / 14762