Sayyiduna al-Ash'ath bin Qays (may Allah be pleased with him) came to Sayyiduna Abdullah (may Allah be pleased with him) on the day of Ashura while he was eating. He said: O Abu Muhammad! Come near and eat. He said: I am fasting. He said: We too used to fast (on this day), then it was abandoned.
There are many reports on this, and all of them negate the special exemption; and Allah knows best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13415