The Sunnah is to fast 9th and 10th. If this was not possible, then one should fast the 10th and 11th.

If this was not possible as well, then one can fast 10th alone.

If a person wants to fast the 3 days together, this is permissible as fasting days of the month of Moharram is a Sunnah

Pls guide-for the month of muharram we fast for two days on 9 and 10 or 10 and 11or is it 3 days 9 ,10 and 11.please inform.