Fasting on the Day of Arafah forgives all prior and the future year sins
TIRMIDHI 749:
from Abū Qatādah —
the Prophet said: "Fast the Day of Arafah, for indeed I anticipate that Allah will forgive (the sins) of the year after it, and the year before it."
الترمذي ٧٤٩:
عن ابو قتاده —
أَنَّ النَّبِيَّ ﷺ قَالَ صِيَامُ يَوْمِ عَرَفَةَ إِنِّي أَحْتَسِبُ عَلَى اللَّهِ أَنْ يُكَفِّرَ السَّنَةَ الَّتِي قَبْلَهُ وَالسَّنَةَ الَّتِي بَعْدَهُ