Bukhari

Hadith Commentary: The days of staying in Mina are the same as those referred to as the Days of Tashreeq, that is, the days of the 11th, 12th, and 13th of Dhul-Hijjah.

Hadith Commentary:
(1)
By the "days of Mina" are meant the days of Tashreeq: the 11th, 12th, and 13th of Dhul-Hijjah.
Since during these days the meat of the sacrifice (qurbani) would be cut and placed in the sun so that it would dry, for this reason they are called the days of Tashreeq.
(2)
It appears that the inclination of Imam Bukhari rahimahullah is that if the one performing tamattu‘ is unable to offer a sacrifice, then he may fast three days during the days of Tashreeq, and the remaining seven after returning home. However, according to the other Imams, it is not permissible to fast during these days.
According to them, if the one performing tamattu‘ is unable to offer a sacrifice, he should also not fast during these days, nor should anyone else fast during them.
Hafiz Ibn Hajar has written:
According to Imam Bukhari rahimahullah, the one performing Hajj tamattu‘ who is unable to offer a sacrifice may fast during these days, because he has presented the practice of Aisha radi Allahu anha, from which his inclination is known.
(Fath al-Bari: 4/307)