Musnad Abu Ya'la al-Mawsili 153:209

Zuhayr narrated to us, Ibn ‘Uyaynah narrated to us, from Ibn Abi Labid, from Abu Salamah, from ‘Abdullah ibn ‘Umar, who said: I heard the Messenger of Allah (may Allah bless him and grant him peace) saying: "Do not let the Bedouins overcome you regarding the name of your prayer. Behold, it is the ‘Isha’ (night prayer), and they (the Bedouins) delay it for the sake of the camels."