Q. May we fast only on the 10th of Muharram?
A. Fasting on ONLY the 10th of Muharram will not be regarded as following the Sunnah. It will be regarded as a Nafl Fast. To acquire the virtue of the Sunnah, one has to fast on the 9th and 10th OR the 10th and 11th of Muharram.
For more questions & answers, virtues and anecdotes pertaining to Muharram, see the following link: https://jamiatnc.co.za/tag/muharram/