Praise be to Allah, and may Allah’s peace and blessings be upon the Messenger of Allah, his family and his companions.   Wa alaikum assalam wa rahmatullahi wa barakatuh.   As to what follows:   In response to your question, we say:   The majority of the scholars are of the opinion that whoever fasts on the day of ‘Ashura alone will get the virtues associated with fasting on this day and that is the expiation of the sins of the previous year. Abu Hanifah was of the opinion that fasting on the day of ‘Ashura alone is detestable because of the hadith that was narrated by ibn ‘Abbas  that the Prophet (peace be upon him)  said, “If I live till the next (year), I would definitely observe fast on the ninth (of Muharram)” [Muslim (1134). However, in reality this hadith cannot be validly used to prove that because ibn Hazm and a group of scholars are of the opinion that the fasting should be on ninth of Muharram and not the tenth.  The Prophet (peace be upon him) said, “If I live till the next (year), I would definitely observe fast on the ninth (of Muharram)”  and he did not mention the tenth. Thus ibn Hazm and a group of earlier scholars understood from the hadith that fasting was for the ninth and not the tenth of Muharram. The correct opinion is that the Sunnah is that a person should fast on the ninth and the tenth of Muharram.  This is the complete form of fasting which a believer should observe so as to combine the evidences, and this is the opinion of the  majority of the scholars. However, if a person fasts on the tenth of Muharram only, and he says, “I cannot fast except for one day. Either I will fast on the tenth or I will not fast at all”. In this situation the person should fast, he is upon goodness and he will attain the virtues of the day by Allah’s Leave. As for the reason for fasting on ninth of Muharram which has been transmitted as being contradicting the Jews in their fasting of the day of ‘Ashura; not all forms of being different from the Jews are compulsory, and not all forms of conformity with them are unlawful. An example of this is: the Prophet (peace be upon him) said, “Pray with your shoes on, be different from the Jews” [at-Tabarani (7165)] . Does this prove the compulsoriness of praying whilst wearing shoes, or the detestability of praying barefoot? The answer is  “no”. However, these things are recommended. This shows us that not every conformity with the Jews is prohibited, and not every instance of being different to them is compulsory. Thus, from this we understand that conformity and non-conformity should be understood in light of other texts. The most complete form of fasting is that a person should fast on the ninth and tenth of Muharram. This is what has been stated by some scholars like ibn al-Qayyim and a group of scholars, to such an extent that ibn Sirin (may Allah have mercy on him) said, “A person should fast on the a day before ‘Ashura and a day after it. However ibn Sirin (may Allah have mercy on him) and some scholars of the past mentioned that this is applicable if the exact date of the month is not known. However, if the month is clear like if the beginning of Muharram was known by the completion of Thul Hijjah (reaching thirty days) or if the crescent for Muharram was sighted then the Sunnah in this condition is to limit the fast to the ninth and tenth of Muharram. This is because  the hadih that discussed fasting for these three days is the hadith of ibn ‘Abbas in the Musnad of Imam Ahmad which states “Fast a day before ‘Ashura and a day after it.” Another narration states: “A day before and after it.” However, this is  a weak hadith according to the majority of the expert hadith scholars. Thus the highest form of fasting for this day, according to the correct opinion, is that a person should fast on the ninth and the tenth of Muharram. The second stage is that a person should fast on this day only, and these are the established stages as evidenced by the legal proofs. If a person is in particular locality where one opinion has gained prominence, and he does not know of any other opinion; this does not mean that the other opinions are not correct, or that there is no other opinion except what he knows.   I say to my brothers, “All praise is due to Allah. Fasting in the ninth, tenth and eleventh of Muharram is part of goodness, because fasting in Muharram is one of the best forms of fasting after fasting in the month of Ramadan, as has been transmitted in an authentic hadith that the Prophet (peace be upon him) was asked as to which was the best month for fasting after Ramadan. He replied, “Fasting in Allah’s month Muharram” [Muslim (1163)]. Thus a person should fast a lot in Muharram. However, we have to clarify that the virtues associated with fasting on the day of ‘Ashura are acquired by a person who fasts on this day alone. A person should observe fasting a day before ‘Ashura because of the Prophet’s (peace be upon him) statement  “If I live till the next (year), I would definitely observe fast on the ninth (of Muharram).