Musannaf Ibn Abi Shayba 3:1501

Abu Mu'awiyah narrated to us, from al-A'mash, from Ubayd Allah ibn Abd Allah, from Ibn Abi Layla, from al-Bara' ibn Azib, who said: The Messenger of Allah (ﷺ) was asked about praying in the resting places of camels, and he said: "Do not pray in them." And he was asked about praying in the resting places of sheep, and he said: "Pray in them, for they are a blessing."