Abdullah bin Abbas (may Allah be pleased with them both) narrates that the Messenger of Allah (peace and blessings be upon him) said: "If I remain safe until next year, I will certainly fast on the 9th."
(Ahmad bin Yunus narrates from Ibn Abi Dhi'b that in the text he (peace and blessings be upon him) said: "If I live, if Allah wills, I will also fast on the 9th, fearing that the day of Ashura might be missed.")
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصيام / 8402