Musnad Abu Ya'la al-Mawsili 34:3

Zuhayr narrated to us, Ya'qub ibn Ibrahim narrated to us, 'Abd al-Malik ibn al-Rabi' ibn Sabrah narrated to us, from his father, from his grandfather, that the Messenger of Allah (may Allah bless him and grant him peace) forbade praying in the resting places of camels, and granted a concession to pray in the sheepfolds.