What is the ruling on entering Mecca for 'Umrah and Hajj without entering into a state of Ihram from the Miqat, and does this necessitate an expiation, especially if the entry is from Riyadh, given that the Malikis are of the opinion that Mecca is a Miqat for its residents and for others?

The Maliki school of thought holds that the miqat (definition) for a Meccan resident performing Umrah (definition) is the nearest point outside the Haram (definition) (known as adna al-hill). If someone from within the Haram performs ihram (definition) for Umrah, they must repeat the tawaf (definition) and sa'i after exiting to al-hill, or offer a sacrifice (dam) according to the majority of scholars. As for the miqat for a Meccan resident performing Hajj, it is Mecca itself.

A visitor to Mecca must perform ihram from the miqat if they intend to perform a ritual (nusuk); otherwise, they must offer a sacrifice (dam) if they perform ihram from within the miqat. If someone comes to Mecca not intending to perform a ritual, but then decides to perform Hajj or Umrah, their miqat is like that of a Meccan resident: for Umrah, they must go out to the nearest point of al-hill; and for Hajj, they perform ihram from their residence in Mecca. If they contravene this and perform ihram for Umrah from Mecca, they must offer a sacrifice (dam).