It is narrated from Qatadah (may Allah have mercy on him) that he heard Sa'id bin al-Musayyib (may Allah have mercy on him) say: The Prophet (peace and blessings be upon him) prayed witr, and it is not obligatory upon you. The Messenger of Allah (peace and blessings be upon him) prayed the Duha (forenoon) prayer, and it is not obligatory upon you. The Prophet (peace and blessings be upon him) offered a sacrifice, and it is not obligatory upon you. He (peace and blessings be upon him) prayed before Zuhr, and it is not obligatory upon you. Qatadah (may Allah have mercy on him) said: I said: These are things that are known, apart from witr. He said: "O people of the Qur'an, pray witr; Allah Almighty is Witr (One) and He loves witr."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 4458