"(She should wait) for the longer of the two periods." Abu Salamah said: "When she has given birth, it becomes permissible for her to remarry." Abu Hurairah came and said: "I agree with my brother's son" -meaning Abu Salamah bin 'Abdur-Rahman. They sent Kuraib, the freed slave of Ibn 'Abbas, to Umm Salamah to ask her about that. He came back to them and told them that she said: "Subai'ah gave birth one day after her husband died;" she mentioned that to the Messenger of Allah and he said: "It has become permissible for you to marry."
Sunan an-Nasa'i Book 27, Hadith 126