Sahih Muslim Book 2, Hadith Number 478.

Chapter : It is commendable to include forehead in washing the face and elbow and ankle in washing the hands and feet, while performing ablution.

Nu’aim b. ‘Abdallah reported: He saw Abu Huraira perform ablution. He washed his face and washed his hands up to the arms. He then washed his feet and reached up to the shanks and then said: I heard Allah’s Messenger (may peace be upon him) say: My people would come with bright faces and bright hands and feet on account of the marks of ablution, so he who can increase the lustre of his forehead (and that of his hands and legs) should do so.