Musnad Abu Ya'la al-Mawsili 110:260

Zuhayr narrated to us, Hashim narrated to us, ‘Imran bin Zayd al-Taghlibi narrated to us, al-Hajjaj bin Tamim narrated to me, from Maymun bin Mihran, from ‘Abdullah bin ‘Abbas, from the Prophet (may Allah bless him and grant him peace), who said: There will be in the end of time a people who will be called the Rafidah; they will reject Islam and cast it out. So kill them, for they are polytheists.