He was asked about the witr prayer, whether it is obligatory.He replied, "Not in the same way as an obligatory prayer, but it is a sunnah practiced by the Messenger of Allah ﷺ and his Companions, who continued upon it until they passed away."
حدثنا أبو معاوية حدثنا الحجاج عن أبي إسحاق عن عاصم بن ضمرة
سئل عن الوتر أواجب هو قال أما كالفريضة فلا ولكنها سنة صنعها رسول الله ﷺ وأصحابه حتى مضوا على ذلك
No references are available.
Its isnad is sahih. Abu Muawiya is Muhammad bin Khazim, the blind, the trustworthy. In H, it appears as Muawiya, which is an error. The hadith is given at greater length at 927.