Abu Hurayrah (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) said: "When anyone of you beats his brother, he should avoid the face."
The Hadīth means that whenever anyone hits someone else for disciplinary purposes, in execution of a discretionary punishment or a corporal punishment prescribed by Allah, the Almighty, or because of a dispute or any other reason, he should avoid hitting the face; even when he is executing one of the corporal punishments prescribed by Allah, the Almighty. This is due to the honor of the human face, as it is the most dignified part of the body and the person deals with others through it. Striking it, therefore, may cause damage to one of its parts or negatively affect it. So this act must be avoided. It is prohibited to strike the face regardless of whether the person deserves to be hit or is hit out of transgression.