It is narrated from Jabir bin Abdullah (may Allah be pleased with him) that the Messenger of Allah (ﷺ) was praying on his camel facing towards the east during the expedition of Banu Anmar.
Hadith Referenceمسند الإمام الشافعي / كتاب الصلاة / 380
Hadith Takhrijأخرجه البخاري: المغازي، باب غزوة أنمار (4140).