It is narrated from Umm Salamah (may Allah be pleased with her) that the Messenger of Allah (peace and blessings be upon him) proposed to her, then mentioned his marriage and spending the night with her, and also mentioned what he said to Umm Salamah (may Allah be pleased with her): "If you wish, I will stay with you for seven days, and likewise with them (the other wives) for seven days."
Hadith Referenceمسند الإمام الشافعي / كتاب النكاح / 1108