It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Observe the fast of Ashura, but oppose the Jews in this matter, and do so by also fasting one day before it or one day after it."
Hadith Referenceمسند احمد / ومن مسند بني هاشم / 2154
Hadith Gradingحکم دارالسلام:إسناد ضعيف ، ابن أبى ليلى، سيء الحفظ ، داود بن على ، يخطئ .