Sahih Muslim 1133
Sahih Muslim · Book 13: The Book of Fasting · Which day should be fasted for 'Ashura?
Hakam b. 'Araj reported:
وَحَدَّثَنِي مُحَمَّدُ بْنُ حَاتِمٍ ، حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ الْقَطَّانُ ، عَنْ مُعَاوِيَةَ بْنِ عَمْرٍو ، حَدَّثَنِي الْحَكَمُ بْنُ الأَعْرَجِ ، قَالَ سَأَلْتُ ابْنَ عَبَّاسٍ - رضى الله عنهما - وَهُوَ مُتَوَسِّدٌ رِدَاءَهُ عِنْدَ زَمْزَمَ عَنْ صَوْمِ عَاشُورَاءَ . بِمِثْلِ حَدِيثِ حَاجِبِ بْنِ عُمَرَ .
I asked Ibn Abbas (Allah be pleased with them) as he was reclining using his cloak as a pillow near Zamzam about fasting on 'Ashura. The rest of the hadith is the same.