Messenger of Allah ﷺ said, "Whoever died and he ought to have fasted (the missed days of Ramadan) then his guardians must fast on his behalf." (Using translation from Bukhārī 1952)  

أنَّ رَسُولَ اللَّهِ ﷺ قَالَ «مَنْ مَاتَ وَعَلَيْهِ صِيَامٌ صَامَ عَنْهُ وَلِيُّهُ»  

“A woman came to the Prophet ﷺ and said: ‘O Messenger of Allah, my sister has died and she owed a fast of two consecutive months.’ He said: ‘Do you not think that if your sister owed a debt, you would pay it off for her?’ She said: ‘Of course.’ He said: ‘The right of Allah is greater.’” (Using translation from Ibn Mājah 1758)   

جَاءَتِ امْرَأَةٌ إِلَى النَّبِيِّ ﷺ فَقَالَتْ يَا رَسُولَ اللَّهِ إِنَّ أُخْتِي مَاتَتْ وَعَلَيْهَا صِيَامُ شَهْرَيْنِ مُتَتَابِعَيْنِ فَقَالَ رَسُولُ اللَّهِ ﷺ «أَرَأَيْتِ لَوَ كَانَ عَلَى أُخْتِكِ دَيْنٌ أَكُنْتِ تَقْضِينَهُ؟ » قَالَتْ نَعَمْ قَالَ «فَحَقُّ اللَّهِ أَحَقُّ»