Musnad Abu Ya'la al-Mawsili 209:118

Abu Khaythama narrated to us, Yahya narrated to us, from Sufyan, from Muhammad ibn Abi Bakr, from Abd al-Malik ibn Abi Bakr ibn Abd al-Rahman ibn al-Harith ibn Hisham, from his father, from Umm Salamah: That the Messenger of Allah (peace and blessings of Allah be upon him), when he married Umm Salamah, stayed with her for three [days]. Then he said: "There is no insignificance regarding you before your family. If you wish, I will stay with you for seven [days], and if I stay with you for seven [days], I will stay with my wives for seven [days]."