What is the ruling, according to Imam Abu Hanifa, on one who enters Mecca without ihram and then assumes ihram from there for Hajj or Umrah?

It is not permissible for anyone intending Hajj or 'Umrah to pass the Miqat without entering into a state of Ihram. If someone does so, they are obligated to return to the Miqat to assume Ihram from there. If they do not return and instead assume Ihram from Makkah, they must offer a sacrifice of a sheep to be slaughtered for the poor of the Haram. This is agreed upon among the madhhabs (schools of thought).

If one returns before entering Ihram, the obligation of the sacrifice is waived by agreement. However, if one returns after entering Ihram, begins the circumambulation (Tawaf), and touches the Black Stone, the sacrifice is not waived because the Ihram has become valid.