Musnad Ahmad 28:248

Abu al-Nadr narrated to us, Muhammad narrated to us, from Sulayman ibn Musa, from ‘Amr ibn Shu‘ayb, from his father, from his grandfather, that the Prophet, may Allah bless him and grant him peace, said: "Whoever bears arms against us is not one of us, and whoever lies in wait on the road [to harm people] is not one of us."