Musannaf Ibn Abi Shayba 9:1552

Abu Usama narrated to us, from Zuhayr, who said: Ali ibn Abi al-A’la narrated to us, from Abu Sahl, from Musah, from Umm Salama, who said: The woman experiencing postpartum bleeding would sit [in seclusion/abstention from prayer] during the time of the Messenger of Allah, peace and blessings of Allah be upon him, for forty days. And we would smear *wars* (a yellow dye) on our faces because of the melasma (dark spots).