Sunan an-Nasa'i, Volume 4, Book 35, Hadith 3847 (DarusSalam) ⓘ

It was narrated that Ibn 'Abbas said: "A woman traveled by sea and vowed to fast for a month, but she died before she could fast. Her sister came to the Prophet and told him about that, and he told her to fast on her behalf."

أَخْبَرَنَا بِشْرُ بْنُ خَالِدٍ الْعَسْكَرِيُّ، قَالَ حَدَّثَنَا مُحَمَّدُ بْنُ جَعْفَرٍ، عَنْ شُعْبَةَ، قَالَ سَمِعْتُ سُلَيْمَانَ، يُحَدِّثُ عَنْ مُسْلِمٍ الْبَطِينِ، عَنِ سَعِيدِ بْنِ جُبَيْرٍ، عَنِ ابْنِ عَبَّاسٍ، قَالَ رَكِبَتِ امْرَأَةٌ الْبَحْرَ فَنَذَرَتْ أَنْ تَصُومَ شَهْرًا فَمَاتَتْ قَبْلَ أَنْ تَصُومَ فَأَتَتْ أُخْتُهَا النَّبِيَّ صلى الله عليه وسلم وَذَكَرَتْ ذَلِكَ لَهُ فَأَمَرَهَا أَنْ تَصُومَ عَنْهَا ‏.‏