Sahih al-Bukhari 4909
Prophetic Commentary on the Qur'an (Tafseer of the Prophet (pbuh))
. "... And for those who are pregnant (whether they are divorced or their husbands are dead), their 'Idda (prescribed period) is until they lay down their burdens, and whoever keeps his duty to Allah and fears Him, He will make his matter easy for him." (V.65:4)
Narrated Abu Salama: A man came to Ibn `Abbas while Abu Huraira was sitting with him and said, "Give me your verdict regarding a lady who delivered a baby forty days after the death of her husband." Ibn `Abbas said, "This indicates the end of one of the two prescribed periods." I said "For those who are pregnant, their prescribed period is until they deliver their burdens." Abu Huraira said, I agree with my cousin (Abu Salama)." Then Ibn `Abbas sent his slave, Kuraib to Um Salama to ask her (regarding this matter). She replied. "The husband of Subai'a al Aslamiya was killed while she was pregnant, and she delivered a baby forty days after his death. Then her hand was asked in marriage and Allah's Messenger (ﷺ) married her (to somebody). Abu As-Sanabil was one of those who asked for her hand in marriage".