Musnad Abu Ya'la al-Mawsili 226:3

Ubayd Allah al-Qawariri narrated to us, 'Alila narrated to us from her mother, who said: I said to Amat Allah bint Ruzaynah, "O Amat Allah, did your mother Ruzaynah narrate to you that she heard the Messenger of Allah (peace and blessings of Allah be upon him) mention the fasting of Ashura?" She said: "Yes, and he used to venerate it, to the point that he would call for his suckling infants and the suckling infants of his daughter Fatima. He would then spit into their mouths and say to the mothers, 'Do not breastfeed them until the night.'"