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)." (TR)
English reference (TR): Vol. 5, Book 44, Hadith 3342 (TR)
Arabic reference (TR): Book 47, Hadith 3665 (TR)