Narrated by Sayyiduna Abdullah bin Abbas (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: Observe fasting on the Day of Ashura, but oppose the Jews in this matter, and that is by fasting a day before it or a day after it.
Hadith Referenceالفتح الربانی / كتاب الصيام / 3929
Hadith Gradingمحدثین:ضعیف
Hadith Takhrij«اسناده ضعيف، ابن ابي ليلي، سييء الحفظ وداود بن علي الھاشمي، قال الامام الذھبي: وليس حديثه بحجة، وذكره ابن حبان في ’’الثقات‘‘ اخرجه ابن خزيمة: 2095، والبيھقي: 4/ 287، (انظر مسند أحمد ترقيم الرسالة: 2154 ترقیم بيت الأفكار الدولية: 2154»
Brief Explanation
Benefits: … This narration is indeed weak, but its meaning appears to be correct: just as one can eliminate resemblance by fasting one day before, similarly, one can do so by fasting one day after, as is the case with the issue of fasting on Friday.
There is no legal (shar‘i) validity to deducing rulings from a weak hadith. (Abdullah Rafiq)