He vowed to fast for an entire month; can he make it Dhu’l-Hijjah?
Question

I made a vow to Allah that I would fast an entire month, but I have not specified which month yet. I thought about it and I decided to fast Dhu’l-Hijjah, because I was intending to fast the first nine days of that month, because they are the best days of the year. My question is: Is it permissible for me to have several intentions (niyyah) at the same time, namely to fast nine days with the intention of attaining the extra reward for them, and also with the intention of fulfilling the vow? Also, I know that it is not permissible to fast on the tenth day of Dhu’l-Hijjah, so if I do not fast on that day, and I fast the rest of the month, will I have fulfilled the vow?
Praise be to Allah.I put this question to our shaykh, ‘Abd ar-Rahmaan al-Barraak (may Allah preserve him), and he said: He can fast the month of Dhu’l-Hijjah and break the fast on the day of Eid and the three days of at-tashreeq (the 11th, 12th and 13th of Dhu’l-Hijjah), then make up those four days after Dhu’l-Hijjah, in Muharram, to make up for the days when he did not fast. End quote.
But when you fast on the ninth day of Dhu’l-Hijjah, the day of ‘Arafat, you should intend the fast to be in fulfilment of the vow, and there is the hope that you will attain both rewards together.
See also the answer to question no. 128256
And Allah knows best.