TIRMIDHI 718:
from Ibn ʿUmar —
the Prophet said: "Whoever died while he had a month to fast, then a needy person should be fed on his behalf in place of every day."
الترمذي ٧١٨:
عن ابن عمر —
عَنِ النَّبِيِّ ﷺ قَالَ مَنْ مَاتَ وَعَلَيْهِ صِيَامُ شَهْرٍ فَلْيُطْعِمْ عَنْهُ مَكَانَ كُلِّ يَوْمٍ مِسْكِينًا