This is from the Oral Torah, recorded in the Talmudic tractate Berakhot 53b. As with Judaism in general, the Oral Torah is considered part of the Torah, and is indicated in the written Torah as having been delivered to Moses on Sinai. Salman and Muhammad both apparently referred to this as the "Torah" as well, and we see numerous Talmudic stories cited, and quoted in the Qur'an.
Monday, April 25, 2011
Narrated Salman al-Farsi: "I read in the Torah that the blessing of food consists in ablution before it. So I mentioned it to the Prophet. He said: The blessing of food consists in ablution before it and ablution after it." (Abu Dawud: Book 27, Number 3752)