The Messenger of Allah ﷺ said, "If I live until next year, I will fast on the ninth day."
حدثني أبو معاوية حدثنا ابن أبي ذئب عن القاسم بن عباس عن عبد الله بن عمير مولى ابن عباس
قال رسول الله ﷺ لئن بقيت إلى قابل لأصومن اليوم التاسع
Its isnad is sahih. Qasim bin Abbas bin Muhammad bin Mutab bin Abu Lahab Hashimi is trustworthy. Ibn Main and Ibn Hibban both affirmed his reliability, and Bukhari mentioned him in al-Kabir 1/1/168, and Ibn Abu Hatim in al-Jarh wal-Tadil 3/2/114.Abdullah bin Umayr is the freedman of Umm Fadl, though his clientage is sometimes attributed to her son Abdullah bin Abbas, and he is a trustworthy successor.The hadith was narrated by Muslim, 1/313, and Ibn Majah, 1/272, both through the route of Waki from Ibn Abu Dhib.