Reference: Siyar A’laam an-Nubalaa – Volume 1, Page 230
Abu ad-Dardaa said:
If we were with the Messenger of Allaah ﷺ on a journey, on a [particularly] hot day – none of us would be fasting except the Messenger of Allaah ﷺ and ‘Abdullaah ibn Rawaahah.
