Musannaf Ibn Abi Shayba 1:1806

Waki’ narrated to us, he said: Sufyan narrated to us, from Musa ibn Abi ‘Aisha, from Sulayman ibn Sa’id, he said: The Messenger of Allah (may Allah bless him and grant him peace) said: "Use the siwak, cleanse yourselves, and perform the witr prayer, for Allah is Witr (One/Odd) and He loves the witr."