Lady Aisha Siddiqa (may Allah be pleased with her) narrates: Whenever the Prophet Muhammad (peace be upon him) performed any deed, he would do it regularly. If he slept at night or could not perform the night prayers due to illness, he would perform twelve rak'ahs during the day. Lady Aisha (may Allah be pleased with her) narrates: I never saw the Prophet Muhammad (peace be upon him) performing voluntary prayers for the entire night until dawn, nor did I ever see him fasting continuously for a whole month except in the month of Ramadan. (Imam Ibn Hibban, may Allah have mercy on him, says:) This narration contains evidence that Witr is not obligatory, because if it were obligatory, he would have performed the thirteen rak'ahs of the night during the day.
Hadith Referenceصحیح ابن حبان / كتاب الصلاة / 2642
Hadith Gradingفضيلة الشيخ الإمام محمد ناصر الدين الألبانيصحيح - مضى مختصرا (2411). تنبيه!! رقم (2411) = (2420) من «طبعة المؤسسة». - مدخل بيانات الشاملة -.فضيلة الشيخ العلّامة شُعيب الأرناؤوطإسناده صحيح على شرط مسلم