Fast on Ashura if one chooses too

Before Islam, the tribe of Quraysh used to observe a day called 'Ashurah by fasting. When Prophet Muhammad ﷺ migrated from Mecca to Medina, he continued this tradition and asked his followers to do so as well. After Ramadan was made obligatory upon Muslims, it became optional for them whether they wanted to fast or not on 'Ashurah. This hadith teaches us that we should respect traditions that are not against Islamic teachings and values even if they are from before Islam came into existence. It also shows us that when something is made obligatory upon us by Allah SWT then we should prioritize it over other things that were previously done out of choice or habit.