Imran bin Husain narrated that:
The Prophet was asked about Ash-Shafi, so he said: "It is As-Salat, some of it is Shaf (even) and some of it is Witr (odd)." (RU)
English reference (RU): Vol. 5, Book 44, Hadith 3342 (RU)
Arabic reference (RU): Book 47, Hadith 3665 (RU)