Sayyiduna Mith'ab (may Allah be pleased with him) said: There was a military expedition with the Messenger of Allah (peace and blessings be upon him), and every one of them had his own mount on which he rode in turns, except me. He said: The Messenger of Allah (peace and blessings be upon him) would dismount and then say to me: "Ride." And I would say: "I have strength," until he did that two or three times, then he said: "You are nothing but a gushing spring (mith'ab)." He said: That became one of my most beloved names to me.
He said: I used to travel with the Messenger of Allah (peace and blessings be upon him) and his Companions, and some of them would fast and some would not fast; the one fasting never found fault with the one not fasting, nor the one not fasting with the one fasting.
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17972