Let us see what He wrote in his book Roda-tul-Motaqeen fi Sharah Man la Yahdaral Faqih


و يويده ما رواه الكليني في القوي، عن نجيه بن الحرث العطار قال، سالت ابا جعفر عليه السلام عن صوم يوم عاشوراء فقال: صوم متروك بنزول شهر رمضان و المتروك بدعه قال نجيه فسالت ابا عبد الله عليه السلام من بعد ابيه عليه السلام عن ذلك فاجابني بمثل جواب ابيه ثم قال: اما انه صوم يوم ما نزل به كتاب و لا جرت به سنه الا سنه آل زياد بقتل الحسين بن علي صلي الله عليهما


And it is supported by what has been narrated by Kulaini in Qawi/strong narration from Najih, He said

: I asked Abu Ja`far عليه السلام about the fast of the day of `Ashura. So he said: An abandoned fast by the revelation of the month of Ramadan. And the abandoned is an innovation (bid`a). Najiyya said: So I asked Abu `Abdillah عليه السلام after his father عليه السلام about that. So he answered me with the like of the answer of his father. Then he said: However verily it is a fast of a day which no scripture has not been revealed with, and no sunna brought about, except for the sunna of the family of Ziyad by the killing of al-Husayn b. `Ali عليهما السلام.


Majlisi I further mentions


و في القوي، عن جعفر بن عيسي قال: سالت الرضا عليه السلام، عن صوم عاشوراء و ما يقول الناس فيه؟ فقال عن صوم ابن مرجانه تسالني؟ ذلك يوم صامه الادعياء من آل زياد لقتل الحسين عليه السلام، و هو يوم يتشام به آل محمد و يتشام به اهل الاسلام و اليوم الذي يتشام به اهل الاسلام لا يصام و لا يتبرك به و يوم الاثنين يوم نحس قبض الله عز و جل فيه نبيه صلي الله عليه و آله و سلم و ما اصيب آل محمد الا في يوم الاثنين فتشاءمنا به و تبرك به عدونا، و يوم عاشوراء قتل الحسين عليه السلام و تبرك به ابن مرجانه و تشام به آل محمد صلي الله عليه و آله و سلم فمن صامهما او تبرك بهما لقي الله تبارك و تعالي ممسوخ القلب و كان حشره مع الذين سنوا صومهما و التبرك بهما


And in Qawi hadeeth from Ja`far b. `Isa his brother. He said: I asked ar-Rida عليه السلام about the fast of the day of `Ashura, and what the people say about it. So he said: You are asking me about the fast of Ibn Marjana? That is the day that the propagandists of the family of Ziyad fasted due to the killing of al-Husayn عليه السلام. And it is the day that the family of Muhammad augur as evil, and that the people of Islam augur as evil. And the day that the people of Islam augur as evil has no fasting and no seeking of blessing (tabarruk) by it. And Monday is an inauspicious day in which Allah made His prophet صلى الله عليه وآله وسلم die in it. And the family of Muhammad are not afflicted but in a Monday, so we augur evil with it and our enemy seeks blessing by it. And on the day of `Ashura عليه السلام al-Husayn was killed and Ibn Marjana sought blessing with it. And the family of Muhammad صلى الله عليه وآله وسلم augur evil with it. So whoever fasts them (two) and seeks blessing by them will meet Allah تبارك وتعالى deformed of heart. And his resurrection will be with those who made their fasts a seeking blessing by them tradition (made them a sunna).


[Rouda tul Motaqeen, 3/248]


There are other narrations which can be found on this link