Language:
كتاب الطلاق
68  
Divorce
(39)
Chapter: "For those who are pregnant, their 'Idda is until they laydown their burdens."
(39)
بَابُ: {وَأُولاَتُ الأَحْمَالِ أَجَلُهُنَّ أَنْ يَضَعْنَ حَمْلَهُنَّ}
Sahih al-Bukhari 5320

Narrated Al-Miswer bin Makhrama:

Subai'a Al-Aslamiya gave birth to a child a few days after the death of her husband. She came to the Prophet and asked permission to remarry, and the Prophet (ﷺ) gave her permission, and she got married.

حَدَّثَنَا يَحْيَى بْنُ قَزَعَةَ، حَدَّثَنَا مَالِكٌ، عَنْ هِشَامِ بْنِ عُرْوَةَ، عَنْ أَبِيهِ، عَنِ الْمِسْوَرِ بْنِ مَخْرَمَةَ، أَنَّ سُبَيْعَةَ الأَسْلَمِيَّةَ، نُفِسَتْ بَعْدَ وَفَاةِ زَوْجِهَا، بِلَيَالٍ فَجَاءَتِ النَّبِيَّ صلى الله عليه وسلم فَاسْتَأْذَنَتْهُ أَنْ تَنْكِحَ، فَأَذِنَ لَهَا، فَنَكَحَتْ‏.‏
Reference : Sahih al-Bukhari 5320
In-book reference : Book 68, Hadith 69
USC-MSA web (English) reference : Vol. 7, Book 63, Hadith 241
  (deprecated numbering scheme)