Sunnah.com reference : Book 8, Hadith 162English translation : Book 8, Hadith 1114Arabic reference : Book 8, Hadith 1103
Narrated al-Miswar bin Makhramah (RA):
Some nights after her husband's death, Subai'ah al-Aslamiyah (RA) gave birth to a child. Then she went to the Prophet (ﷺ) and asked permission to marry. He gave her permission and she married.

[Reported by al-Bukhari].
عَنْ اَلْمِسْوَرِ بْنِ مَخْرَمَةَ ‏- رضى الله عنه ‏- { أَنَّ سُبَيْعَةَ الْأَسْلَمِيَّةَ ‏-رَضِيَ اَللَّهُ عَنْهَا‏- نُفِسَتْ بَعْدَ وَفَاةِ زَوْجِهَا بِلَيَالٍ, فَجَاءَتْ اَلنَّبِيَّ ‏- صلى الله عليه وسلم ‏-فَاسْتَأْذَنَتْهُ أَنْ تَنْكِحَ, فَأَذِنَ لَهَا, فَنَكَحَتْ.‏ }  رَوَاهُ اَلْبُخَارِيُّ  1‏‏1 ‏- صحيح.‏ رواه البخاري (5320)‏.‏