Is it permissible to eat leftover meat bought from a slaughterhouse in Mecca during the Days of Tashreeq, thinking it was cheap, and then it turned out to be Hady (sacrificial) and Adahi (sacrificial) meat?

It is not permissible for the one offering a sacrificial animal (hady) or a Udhiyah (sacrificial animal for Eid al-Adha) to sell their offering, because it is wealth dedicated to Allah. As for someone who acquired the Udhiyah, hady, or fidyah (expiatory sacrifice) through a permissible means, such as receiving it as charity or a gift, they may do with it whatever they wish, including eating it, gifting it, or selling it. Similarly, if an owner slaughters an animal and then leaves it in its place and departs, it becomes permissible for whoever takes possession of it to own it and do with it whatever they wish. Therefore, the general principle is the permissibility of buying from butchers and others, unless it is known that they acquired it unlawfully.