Musannaf Ibn Abi Shayba 3:762

'Umar ibn Ayyub narrated to us, from Ja'far ibn Burqan, from Yazid ibn al-Asamm, who said: It was said to Maymunah, "Do you not see so-and-so pecking his forehead against the ground, wanting to leave a mark of prostration upon it?" She said, "Leave him, perhaps he is salted."