My friend told that there is a hadith about consecutive fasting (Som) according to which consecutive fasting is forbidden, except Ramadan and Shawwal. There must be a gap of one day. We fast on 8th, 9th and 10th Muharram, is this allowed?
Consecutive fasting is not forbidden, but the Prophet advised to fast on alternate days.
You can fast on the 8th, 9th and 10th days of Muharram. There is nothing wrong about it.