Al-Quran

Surah: At-Taubah, Ayah: 37

Surely the number of months with Allah is twelve months in Allah’s ordinance since the day when He created the heavens and the earth, of these four being sacred; That is the right reckoning .

Sahih Bukhari

Hadith on Fasting in Muharram No.609

Narrated Ibn 'Abbas: When the Prophet came to Medina, he found (the Jews) fasting on the day of 'Ashura' (i.e. 10th of Muharram). They used to say: "This is a great day on which Allah saved Moses and drowned the folk of Pharaoh. Moses observed the fast on this day, as a sign of gratitude to Allah." The Prophet said, "I am closer to Moses than they." So, he observed the fast (on that day) and ordered the Muslims to fast on it. حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ اللَّهِ، حَدَّثَنَا سُفْيَانُ، حَدَّثَنَا أَيُّوبُ السَّخْتِيَانِيُّ، عَنِ ابْنِ سَعِيدِ بْنِ جُبَيْرٍ، عَنْ أَبِيهِ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما أَنَّ النَّبِيَّ صلى الله عليه وسلم لَمَّا قَدِمَ الْمَدِينَةَ وَجَدَهُمْ يَصُومُونَ يَوْمًا، يَعْنِي عَاشُورَاءَ، فَقَالُوا هَذَا يَوْمٌ عَظِيمٌ، وَهْوَ يَوْمٌ نَجَّى اللَّهُ فِيهِ مُوسَى، وَأَغْرَقَ آلَ فِرْعَوْنَ، فَصَامَ مُوسَى شُكْرًا لِلَّهِ‏.‏ فَقَالَ ‏"‏ أَنَا أَوْلَى بِمُوسَى مِنْهُمْ ‏"‏‏.‏ فَصَامَهُ وَأَمَرَ بِصِيَامِهِ‏.‏ (SahihBukhari:609)