All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Allah Almighty has enjoined washing the face in ablution. In order to clarify what must be washed in this obligation, it is necessary to know the boundaries of the face; the border of the face is from the roots of the front hair of the head to the bottom of the chin in length [the front end of the two sides of the jawbone] and from the earlobes to the earlobes in width. The criteria is the usual place from where the hair grows, so if one’s hair receded from his forehead [i.e. is bald at the front of his head], then this place that has no hair is part of the head, and whoever has grown hair on his forehead, then the place where this hair grew is part of the face.
The chin is from the face, which is the front end of the two sides of one’s jawbone where the lower teeth grow.
The hair that grows on the sideburns is part of the face. As for the hair that is adjacent to the temporal bone, which is known as the temple, it is from the head and not from the face.
Likewise, the hair that grows at the ends of the forehead is not from the face; rather, it is from the head.
Al-Iqnaa’ reads about the limits of the face:
“The limit of the face vertically is between the roots of the front hair of the head from the hairline to the bottom of the chin, and horizontally, from the earlobe to the earlobe, so it includes the sideburns, which is the hair that grows on the protruding bone of the porous eardrum, and does not include the temple, and it is the hair that grows at the end of the sideburns, that is adjacent to the top of the ear, and descends a little bit, but it does not include the hair that grows at the two sides of the forehead on the sides of the face; nor does it include the two sides of the front hair; rather, all of that is from the head."
Allah knows best.