Musnad Ahmad 1156:25

Ya'qub narrated to us, he said: My father narrated to us, from Ibn Ishaq, he said: Hisham ibn 'Urwah narrated to us, from his father, from Zaynab bint Abi Salamah, from Umm Habibah bint Abi Sufyan, she said: I said to the Messenger of Allah, may Allah bless him and grant him peace: "Will you not marry my sister?" Then he mentioned the hadith.