Musnad Abu Ya'la al-Mawsili 209:100

Abu Khaythama narrated to us, Yazid bin Harun narrated to us, Yahya bin Sa'id narrated to us, from Sulayman bin Yasar, from Abu Salamah bin Abd al-Rahman, that he, Ibn Abbas, and Abu Hurayra were together and they discussed the woman whose husband dies while she is pregnant. Abu Salamah said: "I said, 'When she delivers, she has become lawful [to remarry].'" Ibn Abbas said: "Her lawfulness is the later of the two terms." Abu Hurayra said: "I am with my nephew," meaning Abu Salamah. They sent Kurayb, the freed slave of Ibn Abbas, to Umm Salama and asked her about that. Umm Salama said: "Subay'a bint al-Harith al-Aslamiyya delivered a few nights after the death of her husband. A man from Banu Abd al-Dar, whose kunya was Abu al-Sanabil, proposed to her and informed her that she had become lawful. She wanted to marry someone else, but Abu al-Sanabil said to her, 'You have not become lawful.' So Subay'a came to the Messenger of Allah (peace and blessings of Allah be upon him) and mentioned that to him. He commanded her to marry."