Sa'd b. 'Ubadah asked the Messenger of Allah ﷺ: My Mother has died and she could not fulfill her vow which she had taken. The Messenger of Allah ﷺ said: Fulfill it on her behalf.  

أَنَّ سَعْدَ بْنَ عُبَادَةَ اسْتَفْتَى رَسُولَ اللَّهِ ﷺ فَقَالَ إِنَّ أُمِّي مَاتَتْ وَعَلَيْهَا نَذْرٌ لَمْ تَقْضِهِ فَقَالَ رَسُولُ اللَّهِ ﷺ اقْضِهِ عَنْهَا  

A woman made a voyage and vowed that she would fast one month if Allah made her reach her destination with peace and security. Allah made her reach her destination with security but she died before she could fast. Her daughter or sister (the narrator doubted) came to the Messenger of Allah ﷺ. So he commanded to fast on her behalf.  

أَنَّ امْرَأَةً رَكِبَتِ الْبَحْرَ فَنَذَرَتْ إِنْ نَجَّاهَا اللَّهُ أَنْ تَصُومَ شَهْرًا فَنَجَّاهَا اللَّهُ فَلَمْ تَصُمْ حَتَّى مَاتَتْ فَجَاءَتِ ابْنَتُهَا أَوْ أُخْتُهَا إِلَى رَسُولِ اللَّهِ ﷺ فَأَمَرَهَا أَنْ تَصُومَ عَنْهَا  

A woman came to the Prophet ﷺ and said: I gave a slave girl to my mother, but she died and left the salve-girl. He said: Your reward became certain for you, and she (the slave-girl) returned to you as inheritance. She said: She died and one month's fast was due from her. He (the narrator) then mentioned the tradition similar to the one mentioned by 'Amr b. 'Awn.  

أَنَّ امْرَأَةً أَتَتْ رَسُولَ اللَّهِ ﷺ فَقَالَتْ كُنْتُ تَصَدَّقْتُ عَلَى أُمِّي بِوَلِيدَةٍ وَإِنَّهَا مَاتَتْ وَتَرَكَتْ تِلْكَ الْوَلِيدَةَ قَالَ قَدْ وَجَبَ أَجْرُكِ وَرَجَعَتْ إِلَيْكِ فِي الْمِيرَاثِ قَالَتْ وَإِنَّهَا مَاتَتْ وَعَلَيْهَا صَوْمُ شَهْرٍ فَذَكَرَ نَحْوَ حَدِيثِ عَمْرٍو