A woman came to the Prophet ﷺ and said (to him) that one month's fast was due from her mother who had died. May I fulfill them on her behalf? He asked: Suppose some debt was due from your mother, would you pay it ? She replied: Yes. He said: So the debt due to Allah is the one which most deserves to be paid. (Using translation from Abū Dāʾūd 3310)
عَنِ النَّبِيِّ ﷺ أَنَّهُ أَتَتْهُ امْرَأَةٌ فَقَالَتْ إِنَّ أُمِّي مَاتَتْ وَعَلَيْهَا صَوْمُ شَهْرٍ أَفَأَقْضِيهِ عَنْهَا؟ قَالَ «أَرَأَيْتِ لَوْ كَانَ عَلَيْهَا دَيْنٌ أَكُنْتِ تَقْضِينَهُ؟» قَالَتْ نَعَمْ قَالَ «فَدَيْنُ اللهِ أَحَقُّ أَنْ يُقْضَى»