Maliks Muwatta Book 29, Hadith Number 86.
Yahya related to me from Malik from Yahya ibn Said from Sulayman ibn Yasar that Abdullah ibn Abbas and Abu Salama ibn Abd ar-Rahman ibn Awf differed on the question of a wornan who gave birth a few nights after the death of her husband. Abu Salama said, “When she gives birth to the child she is carrying, she is free to marry.” Ibn Abbas said, “At the end of two periods.” Abu Hurayra came and said, “I am with my nephew”, meaning Abu Salama. They sent Kurayb, a mawla of Abdullah ibn Abbas to Umm Salama, the wife of the Prophet, may Allah bless him and grant him peace, to ask her about it. He came back and told them that she had said that Subaya al-Aslamiya had given birth a few nights after the death of her husband, and she had brought the matter to the Messenger of Allah, may Allah bless him and grant him peace, and he had said, “You are free to marry, so marry whomever you wish.”
Malik said, “This is how the people of knowledge here continue to act.”