When a pregnant widow gives birth, it is permissible for her to remarry
حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا أَبُو الأَحْوَصِ، عَنْ مَنْصُورٍ، عَنْ إِبْرَاهِيمَ، عَنِ الأَسْوَدِ، عَنْ أَبِي السَّنَابِلِ، قَالَ وَضَعَتْ سُبَيْعَةُ الأَسْلَمِيَّةُ بِنْتُ الْحَارِثِ حَمْلَهَا بَعْدَ وَفَاةِ زَوْجِهَا بِبِضْعٍ وَعِشْرِينَ لَيْلَةً فَلَمَّا تَعَلَّتْ مِنْ نِفَاسِهَا تَشَوَّفَتْ فَعِيبَ ذَلِكَ عَلَيْهَا وَذُكِرَ أَمْرُهَا لِلنَّبِيِّ ـ صلى الله عليه وسلم ـ فَقَالَ " إِنْ تَفْعَلْ فَقَدْ مَضَى أَجَلُهَا " .
It was narrated that Abu Sanabil said: "Subai'ah Aslamiyyah bint Harith gave birth twenty-odd days after her husband died. When her postnatal bleeding ended, she adorned herself, and was criticized for doing that. Her case was mentioned to the Prophet (ﷺ) and he said: 'If she does that, then her waiting period is over."'