Reward for fasting Ramadan plus six days of Shawwal amounts to fasting a lifetime

He who observed the fast of Ramadan and then followed it with six (fasts) of Shawwal. it would be as if he fasted perpetually.  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ مَنْ صَامَ رَمَضَانَ ثُمَّ أَتْبَعَهُ سِتًّا مِنْ شَوَّالٍ كَانَ كَصِيَامِ الدَّهْرِ  

I heard Messenger of Allah ﷺ saying like this.  

أَخْبَرَنَا أَبُو أَيُّوبَ الأَنْصَارِيُّ ؓ قَالَ سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ بِمِثْلِهِ  

Abu Ayyub reported a hadith like this (through another chain of transmitters).  

سَمِعْتُ أَبَا أَيُّوبَ ؓ يَقُولُ قَالَ رَسُولُ اللَّهِ ﷺ بِمِثْلِهِ