It is known that the hudud (fixed Qur'anic punishments) are not imposed except on the mukallaf (one of legal responsibility); what is meant by the mukallaf here?

Question:
Honorable Shaykh, may Allah grant you success, it is said that the hudud are not imposed except on the mukallaf. He asks: Is the mukallaf meant to be the one who has reached the age of fifteen?

Answer:
The mukallaf is the adult who is of sound mind; this is the mukallaf, the adult of sound mind. The child is excluded, and the adult who is not of sound mind is excluded.