آداب الخلاف
Abu Hurayrah (may Allah be pleased with him) reported that the Prophet (may Allah's peace and blessings be upon him) said: "If any of you fights, let him avoid (hitting) the face.''
عن أبي هريرة -رضي الله عنه- عن النبي -صلى الله عليه وسلم- قال: «إذا قاتل أحدكم فَلْيَجْتَنِبِ الوجه».
شرح الحديث :
According to this Hadīth, if a person wished to hit another, he must not hit him in the face, because the face is where a person's beauty is concentrated. Also, it is delicate and, thus, any bruising on it would be quite visible.