مِشْكَاةُ الْمَصَابِيحِ
Mishkat al-Masabih 2047
Fasting
Voluntary Fasting - Section 1
وَعَنْ أَبِي أَيُّوبَ الْأَنْصَارِيِّ أَنَّهُ حَدَّثَهُ أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: «مَنْ صَامَ رَمَضَانَ ثُمَّ أَتْبَعَهُ سِتًّا مِنْ شَوَّال كَانَ كصيام الدَّهْر» . رَوَاهُ مُسلم
Abu Ayyub al-Ansari told that God’s messenger said, “If anyone fasts during Ramadan, then follows it with six days in Shawwal, it will be like a perpetual fast.” Muslim transmitted it.
Mishkat al-Masabih, 2047صَحِيح (الألباني)