Hegesippus, quoted by Eusebius (Ecclesiastical History, II.xxiii), describing James the Just (the brother of Jesus and early leader of the church in Jerusalem):

“He was in the habit of entering the temple alone, and was often found upon his bended knees, and interceding for the forgiveness of the people; so that his knees became as hard as camel’s, in consequence of his habitual supplication and kneeling before God.”