The permissibility of fasting on the day of 'Aashooraa. only?

Question: Is it permissible to fast 'Aashooraa. just one day?

Response: It is permissible to fast the day of 'Aashooraa. (tenth day of Muharram) just one day, however, it is better to fast the day before it or the day after it (also) and this is the established Sunnah of the Prophet (sal-Allaahu `alayhe wa sallam) who said: ((If I am (still) here next year, then certainly I shall fast the ninth (day of Muharram))), [(reported by) Muslim, Ahmad, Ibn Maajah, Ibn Abee Shaybah, at-Tahaawee, al-Bayhaqee and al-Baghawee]. Ibn 'Abbaass (radhi-yallaahu 'anhumaa) said: ((along with the tenth (day of Muharram))).

And with Allaah lies all the success, and may Allaah send prayers and salutations upon our Prophet Muhammad (sal-Allaahu `alayhe wa sallam) and his family and his companions.

The Permanent Committee for Islaamic Research and Fataawa, comprising -
Head: Shaykh 'Abdul 'Azeez ibn Abdullaah ibn Baaz;
Deputy Head: Shaykh 'Abdur-Razzaaq 'Afeefee;
Member: Shaykh 'Abdullaah Ibn Ghudayyaan
Fataawa al-Lajnah ad-Daa.imah lil-Buhooth al-'Ilmiyyah wal-Iftaa. - Volume 10, Page 401, Fatwa No.13700

Source: http://www.fatwa-online.com/fataawa/worship/fasting/fas009/0000405_2.htm