“O you who believe! Observing As-Saum (the fasting) is prescribed for you as it was prescribed for those before you that you, may become Al- Muttaqun (V.2:183). Sahih al-Bukhari 4503
Arabic hadith text
حَدَّثَنِي مَحْمُودٌ، أَخْبَرَنَا عُبَيْدُ اللَّهِ، عَنْ إِسْرَائِيلَ، عَنْ مَنْصُورٍ، عَنْ إِبْرَاهِيمَ، عَنْ عَلْقَمَةَ، عَنْ عَبْدِ اللَّهِ، قَالَ دَخَلَ عَلَيْهِ الأَشْعَثُ وَهْوَ يَطْعَمُ فَقَالَ الْيَوْمُ عَاشُورَاءُ. فَقَالَكَانَ يُصَامُ قَبْلَ أَنْ يَنْزِلَ رَمَضَانُ، فَلَمَّا نَزَلَ رَمَضَانُ تُرِكَ، فَادْنُ فَكُلْ.
Translation
Narrated `Abdullah
That Al-Ash'ath entered upon him while he was eating. Al-Ash'ath said, "Today is 'Ashura." I said (to him), "Fasting had been observed (on such a day) before (the order of compulsory fasting in) Ramadan was revealed. But when (the order of fasting in) Ramadan was revealed, fasting (on 'Ashura') was given up, so come and eat."