Abu Dawud
Purification (Kitab Al-Taharah)
Book Number: 001 / Hadith Number: 311
Narated By Umm Salamah, Ummul Mu'minin : The woman having bleeding after delivery (puerperal haemorrhage) would refrain (from prayer) for forty days or forty nights; and we would anoint our faces with an aromatic herb called wars to remove dark spots.