Sahih Bukhari Volume 002, Book 013, Hadith Number 009.
Narated By Tawus : I said to Ibn 'Abbas, "The people are narrating that the Prophet said, 'Take a bath on Friday and wash your heads (i.e. take a thorough bath) even though you were not Junub and use perfume'." On that Ibn 'Abbas replied, "I know about the bath, (i.e. it is essential) but I do not know about the perfume (i.e. whether it is essential or not.)"