When the Messenger of Allah ﷺ fasted on the day of Ashura and commanded others to fast it, the people said, "Messenger of Allah, this is a day revered by the Jews and Christians."The Messenger of Allah ﷺ replied, "When next year comes, if Allah wills, we shall fast the ninth day as well."But the following year did not arrive before the Messenger of Allah ﷺ passed away.In another narration, "If I live until next year, I will surely fast the ninth."Muslim said, In the narration of Abu Bakr, meaning Ibn Abu Shayba his teacher, he said, "He meant the day of Ashura."
حين صام رسول الله ﷺ يوم عاشوراء وأمر بصيامه، قالوا: يا رسول الله، إنه يوم تعظمه اليهود والنصارى. فقال رسول الله ﷺ: فإذا كان العام المقبل إن شاء الله صمنا اليوم التاسع. قال: فلم يأت العام المقبل حتى توفي رسول الله ﷺ. وفي رواية: لئن بقيت إلى قابل لأصومن التاسع. قال مسلم: وفي رواية أبي بكر (يعني ابن أبي شيبة شيخه) قال: يعني يوم عاشوراء.
Muslim narrated it in the Book of Fasting (1134) from Hasan bin Ali Hulwani, who said, Ibn Abu Maryam told us, Yahya bin Ayub told us, Ismail bin Umaya told me that he heard Abu Ghatfan bin Tarif Murri say, I heard Abdullah bin Abbas say [what follows]. The other narration comes through Waki, from Ibn Abu Dhib, from Qasim bin Abbas, from Abdullah bin Umayr, or perhaps he said, from Abdullah bin Abbas, who said [what follows].His statement, "I will surely fast the ninth," means along with the tenth. The tenth is for the fast of Ashura, and the ninth is for opposing the Jews, and this is what Ibn Abbas himself explained. Whoever understands from it that the ninth is meant alone is far removed from the correct meaning, both linguistically and in terms of the style of the statement. So whoever cannot fast the ninth should fast the tenth and the eleventh, because fasting the day after it also falls within opposing the Jews, except that this has not been established from the Prophet ﷺ.As for what is narrated from Ibn Abbas as a saying of the Prophet, "Fast the day of Ashura, and oppose the Jews in it, and fast a day before it or a day after it," this is daif. Bayhaqi narrated it (4/287). In its chain is Ibn Abu Layla, who has poor memory, and he alone transmitted it.The correct position is that it is a stopped report, as narrated by Abdul-Razzaq, and through his route by Bayhaqi (4/287), from Ibn Jurayj, who said, Ataa informed me that he heard Ibn Abbas say, "Fast the ninth and the tenth, and oppose the Jews." Bayhaqi said, "Ubaydullah bin Abu Yazid likewise narrated it from Ibn Abbas."