Sunan an-Nasa'i, Volume 4, Book 27, Hadith 3542 (DarusSalam) ⓘ

It was narrated from Sulaiman bin Yasir that Abu Hurairah, Ibn 'Abbas, and Abu Salamah bin 'Abdur-Rahman were talking about the 'Iddah of a woman whose husband dies, and she gives birth after her husband dies. Ibn 'Abbas said: "She should observe 'Iddah for the longer of the two periods." Abu Salamah said: "No, it becomes permissible for her to marry when she has given birth." Abu Hurairah said: "I agree with my brother's son." So they sent word to Umm Salamah, the wife of the Prophet, and she said: "Subai'ah Al-Aslamiyyah gave birth shortly after her husband died; she consulted the Messenger of Allah and he told her to get married."

أَخْبَرَنَا قُتَيْبَةُ، قَالَ حَدَّثَنَا اللَّيْثُ، عَنْ يَحْيَى، عَنْ سُلَيْمَانَ بْنِ يَسَارٍ، أَنَّ أَبَا هُرَيْرَةَ، وَابْنَ، عَبَّاسٍ وَأَبَا سَلَمَةَ بْنَ عَبْدِ الرَّحْمَنِ تَذَاكَرُوا عِدَّةَ الْمُتَوَفَّى عَنْهَا زَوْجُهَا تَضَعُ عِنْدَ وَفَاةِ زَوْجِهَا فَقَالَ ابْنُ عَبَّاسٍ تَعْتَدُّ آخِرَ الأَجَلَيْنِ ‏.‏ وَقَالَ أَبُو سَلَمَةَ بَلْ تَحِلُّ حِينَ تَضَعُ ‏.‏ فَقَالَ أَبُو هُرَيْرَةَ أَنَا مَعَ ابْنِ أَخِي ‏.‏ فَأَرْسَلُوا إِلَى أُمِّ سَلَمَةَ زَوْجِ النَّبِيِّ صلى الله عليه وسلم فَقَالَتْ وَضَعَتْ سُبَيْعَةُ الأَسْلَمِيَّةُ بَعْدَ وَفَاةِ زَوْجِهَا بِيَسِيرٍ فَاسْتَفْتَتْ رَسُولَ اللَّهِ صلى الله عليه وسلم فَأَمَرَهَا أَنْ تَتَزَوَّجَ ‏.‏