عَنْ ثَوْبَانَ (مَوْلَى رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ) عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَآلِهِ وَسَلَّمَ قَالَ: ((مَنْ صَامَ رَمَضَانَ فَشَهْرٌ بِعَشَرَةِ أَشْهُرٍ، وَصِيَامُ سِتَّةِ أَيَّامٍ بَعْدَ الْفِطْرِ، فَذَلِكَ تَمَامُ صِيَامِ السَّنَةِ))
Mawla of the Messenger, Sayyiduna Thawban (may Allah be pleased with him) narrates that the Noble Prophet (peace and blessings be upon him and his family) said: Whoever fasts during the month of Ramadan, then the fasting of this month (in reward) is equal to the fasting of ten months, and then whoever fasts six days (of Shawwal) after Eid al-Fitr, this entire act becomes equal to fasting for the whole year.