Musnad Abu Ya'la al-Mawsili 87:1

'Abd al-A'la ibn Hammad narrated to us, Hammad ibn Salamah narrated to us, from Sulayman al-Taymi, from 'Ubayd, the freed slave of the Messenger of Allah (may Allah bless him and grant him peace), who said: Two women were fasting, and they were backbiting people. The Messenger of Allah (may Allah bless him and grant him peace) called for a bowl and said to them, "Vomit." They vomited pus, blood, and raw flesh. Then he said, "These two fasted from what is lawful and broke their fast with what is unlawful."