Musnad Ahmad 2703

It was narrated from Ibn ‘Abbas (رضي الله عنه) that The Prophet (ﷺ) used to pray Witr with three (rak'ahs), reciting “Sabbihisma Rabbikal-A'la (Glorify the Name of your Lord, the Most High) (al-A'la 87), “Qul ya ayyuhal-kafiroon (Say (O Muhammad (ﷺ) to these Mushrikoon and Kafiroon): O Al-Kafiroon (disbelievers)" (al-Kafiroon 109) and “Qul Huwallahu Ahad (Say (O Muhammad (ﷺ)): “He is Allah, (the) One)"(al-Ikhlas 112).