TABARANI 1451:
from Thawbān —
[Machine] Narrated from the Prophet ﷺ : "Whoever fasts Ramadan, then follows it with six days of Shawwal, it is as if he has fasted for an entire year."
الطبراني ١٤٥١:
عن ثوبان —
عَنِ النَّبِيِّ ﷺ قَالَ «مَنْ صَامَ رَمَضَانَ ثُمَّ أَتْبَعَهُ بِسِتٍّ مِنْ شَوَّالٍ فَإِنَّ ذَلِكَ صِيَامُ سَنَةٍ»