" On another occasion those of his Companions who were with him heard him exclaim more than once: “O my brethren!” They said to him: “O Messenger of God, are we not thy brethren?” and he answered: “Ye are my companions. But my brethren are amongst those who have not yet come” - in other versions “who will come in the last days”. The way he spoke suggested that he was referring to persons of great spiritual eminence. "

― , Muhammad: His Life Based on the Earliest Sources