Q. Is the correct sunnah to fast on the first ten days of Dhul Hijjah or is it two out of the three days (10th, 11th and 12th), if not please inform me of the correct sunnah?
A. It is commendable to fast during the first ten days of Dhul Hijjah (that is, from the 1st to the 9th of Dhul Hijjah). However, it is not permissible to fast on the 10th, 11th, and 12th of this month. These are the days of Eidul Adha, and it is unlawful to fast on these days.
And Allah knows best.
Mufti Waseem Khan
This answer was collected from DarulUloomTT.net, which is operated under the supervision of Mufti Waseem Khan from Darul Uloom Trinidad and Tobago.