وَعَن ابْنِ عَبَّاسٍ
قَالَ: حِينَ صَامَ رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَوْمَ عَاشُورَاءَ وَأَمَرَ بِصِيَامِهِ قَالُوا: يَا رَسُولَ اللَّهِ إِنَّهُ يَوْمٌ يُعَظِّمُهُ الْيَهُودُ وَالنَّصَارَى. فَقَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: «لَئِنْ بَقِيتُ إِلَى قَابِلٍ لأصومن التَّاسِع»
He said that when God’s messenger fasted on the day of Ashura and commanded that it should be observed as a fast, he was told it was a day held in honour by Jews and Christians, and said, “If I am spared till next year I shall fast on the ninth.”
Mishkat al-Masabih 1950, Book 8, Fasting, Hadith 84. 1 min read