Musnad Ahmad 4003

It was narrated from Ibn Mas'ood that The ones who rode with the Messenger of Allah (ﷺ) on the day of Badr were ‘Ali and Abu Lubabah. When it was the Prophet’s turn to walk, they said to him: Ride, O Messenger of Allah, and we will walk instead of you. He said: “You are not stronger than me and I am not in less need of reward than you."