This hadith has been narrated by Ibn Bishr with the same chain of transmitters (but with a slight variation) that he (the Holy Prophet) inquired of them (Jews) about it (fasting on the day of 'Ashura).

Ibn'Abbas (Allah be pleased with both of them) reported that the Messenger of Allah ( صلی اللہ علیہ وسلم ) arrived in Madinah and found the Jews observing fast on the day of 'Ashura. The Messenger of Allah ( صلی اللہ علیہ وسلم ) said to them: What is the (significance) of this day that you observe fast on it? They said: It is the day of great (significance) when Allah delivered Moses (ؑ) and his people, and drowned the Pharaoh and his people, and Moses (ؑ) observed fast out of gratitude and we also observe it. Upon this the Messenger of Allah ( صلی اللہ علیہ وسلم ) said: We have more right, and we have a closer connection with Moses (ؑ) than you have; so Allah's Messenger ( صلی اللہ علیہ وسلم ) observed fast (on the day of 'Ashura), and gave orders that it should be observed.

This hadith has been narrated on the authority of Ayyub with the same chain of transmitters.

Abu Musa (RA) reported: The day of 'Ashura was one which the Jews respected and they treated it as Id. The Messenger of Allah ( صلی اللہ علیہ وسلم ) said: You also observe fast on this day.

Abu Musa reported that the people of Khaibar (most of them were Jews) observed fast on the day of 'Ashura and they treated it as 'Id and gave their women ornaments and beautiful dress to wear. The Messenger of Allah ( صلی اللہ علیہ وسلم ) said: You (only) observe fast on this day.

Ibn Abbas (RA) was asked about observing of fast on the day of Ashura, whereupon he said: I do not know Allah's Messenger ( صلی اللہ علیہ وسلم ) singling out any day's fast and considering it more excellent than another, except this day (the day of Ashura) and this month, meaning the month of Ramadan.

A hadith like this has been narrated on the authority of 'Ubaidullah bin Abi Yazid.