As for the day of Ashura, the Messenger of Allah ﷺ used to fast it and commanded that it be fasted. When the fast of Ramadan was made obligatory, that practice was abandoned. Abdullah would not fast it intentionally unless it happened to coincide with his regular fasting.
حدثنا إسماعيل أخبرنا أيوب عن نافع
في عاشوراء صامه رسول الله ﷺ وأمر بصومه فلما فرض رمضان ترك فكان عبد الله لا يصومه إلا أن يأتي على صومه
Its isnad is sahih. It is in al-Muntaqa 2216 with similar wording at greater length, and he also attributed it to the two Shaykhs. See also 4349.His statement, "unless it coincides with his fasting," means unless the day of Ashura happens to fall on one of the days he customarily fasted as part of his voluntary fasting.