Musannaf Ibn Abi Shaybah

Hazrat Fatimah bint al-Mundhir says that we were under the upbringing of Hazrat Asma bint Abi Bakr along with her granddaughters. Sometimes, when one of us became pure and started praying, she would notice a little yellowish discharge. Regarding this, we asked Hazrat Asma. She said, "You should refrain from praying until you see pure whiteness."