Is it permissible to fast only the tenth of Muharram?

Fasting frequently in the month of Muharram is among the best deeds, and the best fasting after Ramadan is the fasting of the month of Muharram. Whoever fasts the entirety of Muharram has done well, and whoever fasts part of it will receive a reward commensurate with their fasting, and whoever fasts only ten days will be rewarded. If the "ten" refers to the first ten days of Muharram, then fasting them is good and reward is hoped for, and these are the best tens of this blessed month. There is no doubt about the virtue of these days, as they include the Day of Ashura, which expiates the sins of a year. Al-Hafiz Ibn Rajab mentioned the virtue of the first ten days of Muharram, and that they are the best of Allah's sacred month, and he narrated from Abu Uthman Al-Nahdi that they used to glorify three tens: the last ten days of Ramadan, the first ten days of Dhul-Hijjah, and the first ten days of Muharram. It was also said that it is the ten days during which Allah completed the appointed time for Moses. It was narrated from Wahb ibn Munabbih that Allah revealed to Moses to command his people to repent in the first ten days of Muharram. And from Qatadah that the dawn sworn by in Surat Al-Fajr is the dawn of the first day of Muharram. If the intention is to fast the tenth day alone, it is recommended, but it is better to fast the ninth day with it.