Musnad Ahmad 1279:4

Ya'qub narrated to us, my father narrated to us, from Ibn Ishaq, who said: Muhammad ibn Ibrahim ibn al-Harith al-Taymi narrated to me, from Abu Salamah ibn 'Abd al-Rahman, who said: I entered upon Subay'ah bint Abi Barzah al-Aslamiyyah and asked her about her affair. She said: I was with Sa'd ibn Khawlah, and he died leaving me, and I did not remain except for two months until I delivered. She said: Then Abu al-Sanabil ibn Ba'kak, brother of the Banu 'Abd al-Dar, proposed to me, so I prepared myself for marriage. She said: My brother-in-law entered upon me while I had applied henna and prepared myself, and he said: "What do you want, O Subay'ah?" She said: I said: "I want to get married." He said: "By Allah, you have no husband until you complete the waiting period of four months and ten days." She said: So I came to the Messenger of Allah, peace and blessings of Allah be upon him, and mentioned that to him. He, peace and blessings of Allah be upon him, said to me: "You have become lawful [to marry], so marry."