Fasting on only the 10th of Muharram due to some valid excuse
Q: I have read that it is makrooh tanzihi for one to fast on only the 10th of Muharram (without also fasting on the 9th or 11th). My questions are:
1. What is the ruling if one could only fast on the 10th due to some valid reason?
2. Should he rather not fast on the 10th?
3. What constitutes a valid reason?
4. What's the meaning and ruling of makrooh tanzihi?