Musannaf Ibn Abi Shayba 3:4488

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Shu’bah and Hisham narrated to us, from Qatadah, from Sa’id ibn al-Musayyib, who said: The Messenger of Allah (may Allah bless him and grant him peace) performed Witr, and it is not upon you. I said: Why? He said: The Messenger of Allah (may Allah bless him and grant him peace) only said: "Perform Witr, O people of the Qur'an."