Umaynah said: I said to Amatullah bint Ruzaynah: Did you hear your mother mention anything about the fast of Ashura? She said: Yes, I heard my mother, Sayyidah Ruzaynah (may Allah be pleased with her), say: The Messenger of Allah (peace and blessings be upon him) used to hold that day (Ashura) in great reverence, to the extent that on that day he would call for his own children and the nursing infants of Fatimah (may Allah be pleased with her), put his saliva into their mouths, and say to their mothers: "Do not nurse them until nightfall." And his saliva would suffice them.
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 21074